It is too variable--depends one what breeds are used to make the OE and if the EE is from a hatchery or from Breeder culls.
The range will be from 25 weeks to 30plus weeks--Wellsummer x a blue egg layer will usually take the longest time.
Fastest is Penedesenca x cream legbar.
My EE's and OE's all started laying between five and six months old. None later than exactly six months. Strangely, my welsumers didn't start laying until a little over 8 months, BUT, their daughters, with a cream legbar father, all started at five months. I've noticed my pullets start laying earlier if they are from a late winter or early spring hatch, I've had some start (not EE's though) start at the four month mark.
That's something I'm keeping in mind when I decide when to start chicks.