Just to double check, where do I find the option for the regular maintance in system manager, is it under the data base tab on mail box store?
The exchange online defrager should run by default at 2AM everyday.
Maintance options are at
Administrative Groups->[site name]->Servers->[Server Name]->[Storage Group]
Right click on the store your intreasted in and right click properties then on the database tab. Or you can set it via system policies (mailbox store).