Depends on how stable your rating is 
But you should spend your time on them, don't move until you see the whole line and any time you make a mistake, go over the tactic immediately and understand the solution. Just doing a bunch of tactics probably won't do it very quickly, though you might pick up some tactical patterns that way.
How many tactics do I need to do to get from around 1100 to 1300 in a few mounths. How many/how long should I go for.