About Concurrent H1B

Iam currently working as a full time employee with xxx and billing is 40 hours a week, I would like to know how new employer will match billing hours for concurrent H1B , will it be any issue with USCIS?

New employer will process My Concurrent H1B as a part time example 20 Hours a week

That means weekly 40+ 20=60 hours. is it legal ?
is there any impact while applying a green card process ?

Concurrent employment on H1B is totally legit. There should be no issues with GC due to concurrent employment.