When do you start planning your next flip?

[Vonetta Booker]

For the "serial" rehabbers:  At what stage of a rehab do you start looking and planning for your next flip?  On one hand you want to keep the momentum going (especially since it can be sometimes hard to find a property)--but planning them too close together runs the risk of tying too much of one's money up, correct?  

So, when do you start scouting making offers for the next one?  Do you just wait until the previous one's sold, so that you don't run the risk of carrying multiple properties?