I am saying every 2-3 days to let your corals recover a bit in before going through it again or you can do the whole thing in 1 go this may stress them to much. as your tank is so small. you could upgrade your tank as a xmas gift to yourself and make the sand cleaning a part of the up grade. use your tank water to wash out the sand and then use a bit of new salt mix to rinse the sand before adding to the new tank. other things you can do is put everything a large tough toot and do a sand cleaning and rinse with new salt water mix. one other thing I didn't remember to let you know when you clean a new area you should give the area that you have already cleaned a once over.

After carfull thought I have changed my opinion as to what I would do. My self I would do the large tough toot idea or upgrade to a larger tank. It would take less time and way less work. As it seems that you are cleaning only a very small area. This way all you would have to do is siphon as regular maintenance.

I am giving you more options as we go.
Bill