Actually, time is not necessary relevant in this issue.
But first, make sure you are OUT of the last one before you move on. Once you are free and clear, (may be except for the nastalgia) then you actually control the time frame by the way you spend your time. i.e. the selection of activities.
Also, please do try
not to compare the may be's with the ex. I personally hated this with passion. It's just plain non constuctive. You should try to look at each may be like your first love, from scratch. Otherwise, you are looking for a replacement with improvments.
If you're an average guy, I'll say 3-4 months is the norm. That should be enough time for all the sulking, mourning, healing, reality to set in...... etc etc. But what the heck, you never know who pops up just when you think you NEED more time. So keep your head up, eyes open and put on your best face. Good luck.