How Much Time Should Be Left Between 1st and 2nd Treatment of Sclerotherapy?

I would wait 3-4 weeks between sclerotherapy treatments.  This will allow enough time for bruising to resolve.  

Sclerotherapy can be done 2-6 weeks apart but usually is done 4 weeks apart and require 2-3 sessions as an average but some stubborn varicosities need 4-6 sessions.  Support hose is very helpful in resolving the varicosities quicker.  Most sessions run $350-450 each and are done with pilodocanol or foam sotradecal.  Hypertonic saline isn't used much anymore.

Usually sclerotherapy is scheduled a few weeks apart, but it totally different areas are done on a future treatment, then it might be appropriate to do the untreated area as early as a couple of weeks after the first.