Pitch more yeast. If I don't see activity / krausen by end of day 3 for a lager, I'd pitch more yeast. I make lots of lagers and it is not unusual to wait 3 days for activity. By then, though, I see yeast rafts starting to form on the top of the beer. It's a good idea to have some dry yeast around just for this purpose (I like W34/60 for lagers).
Regarding the hydrometer, of course that is a good idea, but the krausen and bubbling airlock are my indicators. I've made enough beer to know what to expect, at least with my equipment.