I would like some advice to make the journey from cow hollow(Lombard street) to the visitor center by renting a bicycle. Is it a difficult path for a beginner? How much time is required?

Was just in a tour there recently and we took a bus with a tour company. The road was very steep, narrow, and winding. Unless you are very comfortable and skilled on a bike, I wouldn't recommend that method to get to Muir Woods. Sorry can't say on the time to get there, but I imagine it would take a while as a beginner on those hills.

It is difficult

Thanks for your suggestions! Ultimately I decided to walk the dipsea trail! Quite challenging but affordable with due caution! Many steps!

It is not difficult. It is an easy walk, with very nice views