Having a new model HD, as TQ says probably just a couple minutes, 'bout the time to put on your helmet and riding gear and take it easy before "reving it up to full highway speed.
Being as I have a carbureted model, I have to do this out of necessity, with the choke on full for about 1 minute, 1/2 for 2-3 minutes and off by the time I hit the local freeway and cruise initially at about 45-55, because the bike would sputter and back fire if I tried to speed up the process.