More efficient way to do this SQL Procedure

I am creating a stored procedure that is used by another program.  The procedure is very slow for large databases, and I wanted to see if there are suggestions on making it faster.   Each entry in the database has a time stamp, which is not necessarily unique.  Some rows share the same time stamp.   I want to get a list of the distinct timestamps for which a list of conditions is true for that time stamp (across multiple rows).   I first select data from the database data to populate a @searchTbl by selecting rows in the table that have either a specific User, Var3, and/or Time (if these are sent to the procedure and so are not NULL).  If the user does not send a specific time (If NULL), I get the latest entries for each unique combination of certain variables (Var4, Var1, Var2, Var3).  I then eliminate rows from the @searchTbl by selecting terms from a conditions table (@condTbl) to create a new select statement.  For each recursive loop, I put the new selection into a @loopTbl, then delete from the @searchTbl, then populate the @searchTbl with the @loopTbl data, then delete the @loopTbl data (I know this is embarrassingly inefficient).

Is there a way to accomplish all of this more efficiently without using the @searchTbl and/or @loopTbl?   I think this might be why it's so slow, because I have to put nearly the whole database into the @searchTbl to begin. 

EDIT NOTE:  SEE MY RESPONSE DOWN THE PAGE FOR THE STORED PROCEDURE DDL

The code to create the table types is listed below the procedure code:

Gina

DECLARE @ProjectTable nvarchar(128)
SET @ProjectTable = 'RIProj_HCT'
DECLARE @CondTbl conditions_tbltype READONLY
DECLARE @UserName nvarchar(255) = NULL
DECLARE @eTime datetime = NULL 
DECLARE @Var3 nvarchar(255) = NULL
DECLARE @SQL nvarchar(4000)
DECLARE @whereAdd nvarchar(4000)
DECLARE @Var4 nvarchar(255)
DECLARE @Var4Var3Time nvarchar(255)
DECLARE @Var1 nvarchar(255)
DECLARE @Var2 nvarchar(255)
DECLARE @CondSign nvarchar(30)
DECLARE @ValType nvarchar(255)
DECLARE @VarTxt nvarchar(4000)
DECLARE @VarNum float
DECLARE @c int
DECLARE @condCt int
SET @condCt = (SELECT count(*) FROM @CondTbl)
DECLARE @SearchTbl tempSearchTbl_tbltype
DECLARE @LoopTbl tempSearchTbl_tbltype
IF (object_id(@ProjectTable) is NULL)
           BEGIN
              RETURN
           END
              SET @whereAdd = ''
              IF @Var3 IS NOT NULL
                 BEGIN
                     SET @whereAdd =  @whereAdd + ' AND Var3 = @Var3'
                  END
              IF @UserName IS NOT NULL
                 BEGIN
                     SET @whereAdd = @whereAdd +' AND UserName = @UserName'
                     END
              IF @Time IS NOT NULL
                 BEGIN
                     SET @whereAdd = @whereAdd +' AND eTime = @eTime'
                 END
              ELSE
                 BEGIN
                     SET @whereAdd = @whereAdd +' AND NOT EXISTS (SELECT 1 FROM ' + @ProjectTable + ' WHERE
                     Var4 = p.Var4 AND Var1 = p.Var1 AND Var2 = p.Var2 AND
                     Var3 = p.Var3 AND Time > p.eTime)'
                 END
              SET @SQL = 'SELECT Var4, UserName, Var3, Var1, VarNum, VarTxt, NForm,
                                     Var2, eTime, Var4Var3Time FROM ' + @ProjectTable + ' p WHERE 1 = 1' + @whereAdd
              INSERT INTO @SearchTbl (Var4, UserName, Var3, Var1, VarNum, VarTxt, NForm, Var2, eTime,
                             Var4Var3Time)
                     EXEC sp_executesql @SQL,
                         N'@Var4 nvarchar(255), @UserName nvarchar(255), @ProjectTable nvarchar(255),
                           @Var3 nvarchar(255)',
                         @Var4, @UserName, @ProjectTable, @Var3
 ConditionLoop:
              IF @condCt >= 1
                 BEGIN
                     SET @c = 1
                     WHILE @c <= @condCt
                         BEGIN
                             SET @Var1 = (SELECT Var1 FROM @CondTbl WHERE cID = @c)
                             SET @Var2 = (SELECT Var2 FROM @CondTbl WHERE cID = @c)
                             SET @CondSign = (SELECT condSign FROM @CondTbl WHERE cID = @c)
                             SET @ValType = (SELECT ValType FROM @CondTbl WHERE cID = @c)
                             SET @VarTxt = (SELECT ValTxt FROM @CondTbl WHERE cID = @c)
                             SET @VarNum = (SELECT ValValue FROM @CondTbl WHERE cID = @c)
                             SET @SQL = 'SELECT * FROM @SearchTbl WHERE Var4 + CONVERT(VARCHAR(100), Time, 121) IN
                                     (SELECT Var4 + CONVERT(VARCHAR(100), Time, 121) AS TagTime FROM @SearchTbl'
                             SET @SQL = @SQL + ' WHERE Var1 = @Var1 AND Var2 = @Var2'
                             IF @ValType = 'Num'
                                 BEGIN
                                     SET @SQL = @SQL + ' AND VarNum ' + @CondSign + ' @VarNum'
                                 END
                             IF @ValType = 'Text'
                                 BEGIN
                                     IF @CondSign = 'LIKE'
                                         BEGIN
                                             SET @SQL = @SQL + ' AND VarTxt LIKE @VarTxt'
                                         END
                                     IF @CondSign = 'NOT LIKE'
                                         BEGIN
                                             SET @SQL = @SQL + ' AND NOT VarTxt LIKE @VarTxt'
                                         END
                                 END
                             SET @SQL = @SQL + ')'
                             DELETE FROM @LoopTbl
                             INSERT INTO @LoopTbl
                               EXEC sp_executesql @SQL,
                                 N'@SearchTbl tempSearchTbl_tbltype READONLY, @Var1 nvarchar(255), @Var2 nvarchar(255),
                                 @Time datetime, @Var3 nvarchar(255), @UserName nvarchar(255),
                                 @VarNum float, @VarTxt nvarchar(4000), @CondSign nvarchar(30)',
                                 @SearchTbl, @Var1, @Var2, @Time, @Var3,
                                 @UserName, @VarNum, @VarTxt, @CondSign
                             SET @c = @c + 1
                             DELETE FROM @SearchTbl
                             INSERT INTO @SearchTbl SELECT * FROM @LoopTbl
                         END
                 END
 FinalReturn:
     SELECT DISTINCT eTime FROM @SearchTbl
     RETURN

Code to create the table types used in this procedure:

CREATE TYPE conditions_tbltype AS TABLE (cID int, Var1 nvarchar(255) NOT NULL, Var2 nvarchar(255) NOT NULL, condSign nvarchar(255) NOT NULL, ValType nvarchar(255), ValTxt nvarchar(4000) NOT NULL, ValValue float)
CREATE TYPE tempSearchTbl_tbltype as TABLE (Var4 nvarchar(255), UserName nvarchar(255), Var3 nvarchar(255), Var1 nvarchar(255), VarNum float, VarTxt nvarchar(4000),NForm nvarchar(255), Var2 nvarchar(255), eTime datetime,
Var4Var3Time nvarchar(255))