I just got this plant today and it already had a lemon when I bought it.
Is This Improved Meyer Lemon Ripe?
Certified GKH Gardening Expert
Here are some guidelines you can go by to determine ripeness of lemons:
* color - fruit should be yellow, with maybe a small amount of remaining green at the end.
* squeeze test - it should give somewhat to pressure when squeezed.
* roundness - Meyer lemons tend to get rounder when they are ripe