A delay of 0 never reschedules, actually, unless there's a better priority
thread. A greater delay depends on if a >= or similar check matches, but
generally is at least 200us.
It seems like this actually completes in at least another 10-20us.
Turns out it's a deadline to wake up by, which makes sense.
sceDisplayWaitVblankStartMultiCB 10
-> Callback
sceDisplayWaitVblankStartMultiCB 2
+2 vblanks
<- Thread
+8 more vblanks
