I would try
[objectStartTime > '[%CurrentDateTime%] - objectDurationHours * [%HourLength%]']
Hopefully doing the calculation on the right-hand side with the current datetime will mean a single calculation, rather than a calculation for each record
Note that the tick marks start before [%CurrentDateTime%] and end after [%HourLength%]
This is for instance valid: [Datum < '[%CurrentDateTime%] + 1 [%DayLength%]']
see also link text
You'll need to use a seperate attribute where you save this time/date.
module.enddate = addHours(objectStartTime, objectDurationHours)
You can then use
[module.enddate < '[%CurrentDateTime%]']