If I am in a credit spread strategy like bear call spread; and I close the position on say tuesday, can I enter in a new credit spread of different strikes on the same day ? Or do margins remain blocked for the entire day ?
The margins blocked are released immediately in your account when you exit the position, and you can use these to take positions on same day.
However, the funds which you will receive from Selling Option position can only be used to take Long Option position in same segment, for all other trades this can be used from T+1 day.
When selling put credit spreads, what are the ways to find price pairs for the best risk-reward ratio?
There is no standard for that.