In answer to your original question, I would say stick by the schedule.
Of course if you have reviewed, and written out all of the kanji that mnemosyne has given you and you want to do a few more then there is no harm in doing it every now and then, but the schedule was put there in the first place to help your memory so I wouldn't do it all of the time.

Guys, I am practicing writing the Kanji and everything, I'm just using the SRS to oremember them.