That info usually isn't available on the download page. Check the forum for the game for reviews, and also the Gamezebo website which usually has nice thorough reviews. I would hope that the BFG walk through would mention it as well, for games that have a walk through. Since most games I don't check the walk through I can't promise about it.
I've thought of more HOGs that have no timers since the list above, but that's enough to keep you busy for a long time. If you are looking at a game and can't tell, try posting in the forum for the game asking, or send me a PM and if I have time I'll re-download it and check. I've purchased most of the no-timer HOGs that BFG offers.