From dry after a rebuild it can take a while to get pressure.
As UK-Vstrom 650 said pump ,release bleed nipple ,close,release lever slowly,repeat.
And as you have done tying back the lever overnight will help,but more as a last little bit,to firm it up.
I always put the master cylinder cap loosely back on when pumping and cover the tank.
That brake fluid is baaad on paint.(don't ask how I know)
As long as you don't have fluid coming out somewhere( worth a check) it will come.