In the power supplies section of the FAQ, this will be answered.
If it´s a standard ATX board your trying to power, my suggestion is an opus. They´re [all] usually selectable for pre-defined startup and shutdown timers that can be adjusted, the amount and duration is just limited by what they´ve set the micro-controller for each to be able to do. Opus seems to have better options where this is concerned, at least in my limited experience.
My opus 360 for example I have set to run 15mins after the ACC line (or IGN if you want to use that) is cut. And starts 5 seconds after power is supplied (steady) to ACC, with a higher than usual undervolt setting for actual startup (not counting the cut-off setting), so it doesn´t come on unless the battery is at a certain level even if power is sensed on the ACC line.