When we went on a Saturday at 8am, there was already a long line but most people were getting gear for the Narrows. I'd still suggest going close to open if you're going on a weekend.
I believe they open at 7am on weekdays - would suggest that you go at open just to be sure that you get to rent what you need. We rented gear for the Narrows and got there at opening on Monday and had 8 people in front of us.
I am not sure but I did see alot of bikes and helmets there for rent.
Thanks! Your answer is awaiting moderation.