However , i may stop by briefly but rather late if it won't be too late by the time we finished
Your sentence is a little unnatural. It would read better as "However, I might stop by briefly later, if it's not too late by the time we finish".
Note the corrections I made to your post above. With English punctuation:
- Start every sentence with a capital letter.
- End every sentence with a single appropriate punctuation mark.
- Do not put a space before a comma, a full stop, a question mark or an exclamation mark.
- Put a space after a comma, a full stop, a question mark or an exclamation mark.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.