I have a Big Max pumpkin that sprouted a little over a month ago. It's looking good and producing lots of leaves, but I haven't seen the first sign of buds anywhere. I've never done pumpkins before, so I'm not sure when I should expect to start seeing blooms.
I don't know about Big Max, specifically, but I believe that 40-55 days is the general time from pollination to fruit maturity for pumpkins. Extrapolating on that and the 110-day time to maturity for Big Max, I would assume that you would expect pollination to happen around 7-8 weeks after seed germination.
If you look at the vines, you should be able to see the little flower buds that will develop into flowers along the main vine, close to the base of a leaf. My pumpkins (Jack be Quick this year) first started showing buds around the 28 day mark.
Edit: If you want to read more about the effects of fertilisation on pumpkins, this paper on the subject is one I found helpful. It has some excellent information, but be sure to note that they were dealing with commercial-size plots and were using a fairly rigourous fertilisation schedule. As such, their anthesis/fruit dates should be expected to come sooner than a garden that isn't as closely monitored. Also, the paper uses data based on the Libby Select variety, which has an average maturation time of 105 days.