math.. how long is to long?

Ok.. I’ve discussed with this board before my math issues.. but I’ll sum it up.  We are doing MUS.  We like it and it works.  I have no doubt with that part.

My one son who is 10 struggles in math terribly.  We stopped moving forward and went backward to help re-force the older stuff ei. addition and subtraction.  Now we’ve been in gamma for over a year (or more like not in) and are just getting back to working on multiplication.

I know this was the best thing to do for him.  He’ll never get anything in math if the basics + & – were not there.  Now were going to go back in to the gamma book redo it from the beginning.

So my question.  How much time both at one time and through out the day are to much?  Here’s my thought.  I’d like to have him work on the gamma as usual during school time (about 10-15min).  Then during the little ones nap time I’d like him to do maybe 3-5 online drills of + or – just to keep these fresh in his mind.  Then in the evening like 3 min of online drilling of the current gamma he’s on.  Does this seem to much?  It wont be every day cause it just wouldn’t be possible every day.  But lets say 4 out of 7 days.  With the online drills I’m not looking for time (well within reason, his 10 is non exsistant), but am looking for 100% on facts.

Please let me know what you think.  This child forgets things if he isn’t constantly reminded of them.   I can’t think of any other way to do it.  What I would really like is a game.  But I have not found one that would work for him.  Any other suggestions would be great.  Thanks everyone! Misty