walk-up arrival time

[mrk00k]

I'm planning on stopping off in Yosemite in a few weeks (Friday 3/12), but am a little concerned. What time should I arrive by to get a walk-up site at Upper Pines? I will be traveling on my motorcycle so its pretty important I find a place to sleep. Are there any good alternatives in the area that I could use as a backup plan?

Alternatively, since it is just me, one small tent, and my motorcycle, do you think I could just ask people to crash on their site for $10 or something like that?

Thanks in advance.