Title is the question 

X2 on this advice.There are several signs of oncoming egg production:
- Redder, larger combs and wattles.
- "Squatting" as you reach down to pick the bird up. Squatting is the natural response of a hen who is ready to mate with a rooster.
- Investigating the nest boxes frequently.
- Cackling for no apparent reason.
- Sometimes a change in voice to a deeper sound.
If you see any/all of those signs, chances are you will get eggs in 1-4 weeks.