Time out of Academic Environment (Mathematics)
This seems to me like a situation in which it is better to "go for the gold". Delay doesn't sound like a backup plan, actually. If you've been accepted and it is something that you really want to do, then just do it. 

I suspect that it will work out better if you start sooner. If, on the odd chance that it doesn't work out, develop a backup at that point. But being overly cautions now might make it harder to achieve your actual goals. 

Take the offer that seems best to you. Make it work. It would place you better for a later doctoral program than delay would and you have no guarantee that you would be able to advance in important areas if you delay.