Figure around 10 week after the plant was germinated.
If you start seeing pumpkins any time now through early august you should be fine.

I hand pollinated my first female flower August 18th last year on a Connecticut Field. That one was 45#, and orange a couple weeks before Halloween. I think if you're seeing some now, you are supposed to shade them so they don't go orange too early.

Really all pumpkins should be shaded and not in sunlight for best results.
The pumpkin does not need sunlight, the leaves do.