When sentenced to community service, can this be deferred and performed 6 months later, and must it be performed in the county where the crime was committed?

This is left to the discretion of the judge.
You will have to request it from the court.

It must be done in the time frame that the court gives you, you will not be allowed off probation till it is done.

It can only be done where and in what places are approved by that court, some will allow it to be with religious groups, others will not.

The thing is why do you want to wait, get it over with, the longer you wait, the more you will put it off