Actually have found that for my kids and for myself immersion in a subject is a great way to learn. There was a year when my ds was 9-10 where math was his only area of formal academic study; he learned brilliantly. My dd has had years devoted almost entirely to music. But I think it's crucial that the desire for that intensive approach come from the child. If your kids are excited about math, and/or are keen to really dive in and make progress, and/or enjoy working at it, this could be a great approach. I find that when we do something like this there's often a big spill-over of learning into other areas, because optimistic engaged kids are great natural learners. So while my ds was working on all that math, he improved in his handwriting and reading and all sorts of other things. Capitalizing on enthusiasm is always a great thing.
If on the other hand your kids resist math and dislike it, I think that unless there's some very dire reason why they need immediate remediation you might run into big problems with this. Nobody likes doing stuff they know they're not good at, especially if it's squeezing out the stuff they enjoy and feel successful at. If you have a kid who loves reading, history and electronics, but lags in math, I think you'd be far better off milking those areas of enthusiasm for ways they might intersect with math, rather than saying "sorry, until you fix your math lags, no more of the stuff you enjoy."
If your kids don't much like math, or feel unsuccessful at it, I would work on trying to fix those feelings by changing how you approach it. Come at it from their area of interest. Mix things up, make it more playful, involve your kids in discovering ways to make math meaningful and enjoyable.