Depending on the OG, I would start checking either at 2 or 3 weeks from start of fermentation (or when it went visible) not from when you pitched the yeast. Although, I typically have active signs within 12 hours of pitching the yeast...
How I typically plan my brews:
OG under 1.050, check after 2 weeks (how much after is up to you.
OG from 1.050 to 1.065, check after 3 weeks.
OG from 1.065-1.085, check after 4 weeks.
OG above 1.090, might take one reading at 4-5 weeks... All depends on the brew and such...
With all the readings you take, taste the sample once you've taken the hydrometer reading. If you detect any off flavors, then leave it on the yeast cake. I've bulk aged my bigger brews, so far, for about a month, or more... So far, the final elements have been oak chips, with one getting a bourbon soaked vanilla bean before that. I racked off the bean to halt it's addition to the brew. It's bottle conditioning now, having sampled one over this past weekend. I'm planning on letting them bottle condition/age for at least a month before I try another one. I might go two months.