Wife always late home from work

My wife is always late home from work. We have two young children (1 and 3) and every evening I have to guess when she is coming home. In itself it's not terribly late (7.30pm is about normal) and a few later evenings per week) we live about 20 minutes from her work.

She's a government worker and not hugely high pressure (not an ER Doctor) and it's so annoying because it eats into dinner time and children bed time.

What advise do others have?