From my own experiences (about a year ago) I'd suggest the following:
Time to get used to them: About 2 hours
Time to get REALLY used to them: About 2 months
The trick is (whenever possible) to move your head, rather than your eyes. If (when you've first got your varifocals) you try to look down at the pavement immediately in front of you by moving your eyes, everything will 'swim about', inducing something akin to travel sickness. To avoid this rather unpleasant sensation you need to tilt your head forwards, so that you're still looking through the middle of the lenses, rather than through the lower portion (which is for close up vision).
Chris