how long til egg #2?

we got our first egg yesterday *yay*...it was on the small side, but had a nice hard shell, even color...my daughter accidently dropped it a few minutes later but before that it looked perfect. There was a little glob of redish brown blood next to the yolk...but I assume thats ok??
So when can we expect more eggs? Not sure which chicken laid it. We have a plymouth rock, delaware, Australorp, buff orph. and a red star.

Once they start laying is it a fairly regular thing or will # 2 take awhile? They are 4 months old btw

 

ok I counted the weeks...they are all 17 1/2 weeks old.

I keep a heat lamp in there 24/7 ( they are spoiled I know) could that be whats helping it along? It's usually in the 50-60's during the day and 30's-40's at night so I keep it on most of the time ( always at night)

 

got number 2 today...I posted a pic in the "first eggs" thread.

 

and another this morning! eating them both right now....yum!