Yes, it's there. In VidCap go to Options / Preferences / Capture. Put a checkmark next to Maximum capture length and enter the duration of the capture. This will automatically stop the capture at that duration.
What would be nice is an option to defer starting the capture until a specific time. SoundForge just got this ability for the recording dialog in version 7. Hopefully the next version of VidCap will have this too. It's so close with the capture delay option, but that only allows a maximum of 10 seconds. Oh well.