I am having an issue in trying to get a selection statement completed.

I have 3 fields and 4 parameters I am trying to work with:
txdate(date) i.e. 9/26/2012
labstarttime(string) i.e. 0584
endstarttime(string) i.e. 1426
[?]startdate
[?]enddate
[?]starttime (2 options; 0600 or 1800)6am to 6 pm shifts
[?]endtime (2 options;0600 or 1800) 6am to 6 pm shifts

I think I have it all with this selection formula:
{PV_JobCosts1.LabEndTime} < {?EndTime} and
{PV_JobCosts1.LabStartTime} > {?StartTime} and
{PV_JobCosts1.TxnDate} in {?StartDate} to {?EndDate}

BUT I have found a few transactions that do not pass muster. My parameters are ?StartDate and ?Enddate are 9/26/2012 and ?starttime=0600 and ?endtime=1800.

I have two records that come up up with:
date,starttime,endtime
9/26/2012,2344,0000
9/26/2012,1929,0000

I am sure the endtimes being 0000 are the problem, but I am not sure how to correct it.

Does anyone have any good thoughts?

They do not necessarily want to only see it by shifts. They may want to just look at one shift or they may want it to run for a "24 hour" period (6am to 6am) or they may want to look at it for a week (Sunday to Saturday).