In sci.electronics.basics Jim Thompson wrote:
Anyone make an off-the-shelf timer that I can trigger and it'll run
for X-hours then operate a relay?

Or do I have to roll my own?

You can buy them. I'd start with Panasonic- they're cheaper than omron,
and usually less complex to deal with.

their support is complete garbage though, not that you'd need it for a
timer. Keep in mind that programming the digitals ones can be infuriating
and involves map folded, poorly translated, japanese sofware logic with
bonus 7 other irrelevant dead languages datasheets.

here's the start page

http://pewa.panasonic.com/automation-controls/timers/

If accuracy is not critical, the versions with dial are easy.

these things tend to be cheapest off ebay of all places. Grainger will
take you for a serious ride if you go that route.