How long should it take for germinated seeds to break the surface?

70f wouldn't cause them to fail, no worries there. i have germed seeds at 68f in winter no problem. if tamped down a little harder, might take more time.. deeper, same thing.... i'd give it at least 9-10 days (two weeks if planted directly into substrate, since you aldo need to count time to germinate). i know some won't like what i say -- adding extra steps just to see a taproot increases risks... incontrovertibly true... a maathematical certainty. in addition to normal reasons why it might take longer to breech surface, it now could have been infected by your fingers touching tap root... or anything else invovled in the extra steps that would normally not be part of the process. even so, it doesn't diminish percentages any noticeable amount, if careful. if you must see the tap root pop out, go ahead and keep doing it this way. if oyu can simply pop them into some substrate and ignore than for 2-3 days, that's a better route, imho. fewer opportunities for something bad to happen... inarguably true.