J.S.
Wow, C.!! That's a GREAT question! I have a friend who owns a babysitting service, but obviously, the sitters/ nannies CAN'T cheat on their hours!
Are the clients ever at home when the cleaners arrive? If they are, then I would ask the CLIENT to call the office (or set up a special # just for this purpose, to leave a message) when the cleaners arrive and leave the client's home.
I don't know if there is any way of "electronically" keeping track of their time, either. Your friend might want to call the Secretary of State for Texas, and ask how she can keep better track of her employees' time.
Wish I had a better answer for you!! I hope this helps some...