I don't know that this is a good idea.

I would say it's definitely a bad idea for a white belt. The first year of BJJ should be continuous. Otherwise, after the break, the trainee will have lost a lot of the knowledge and habits. I've seen this happen at least ten times, but I have yet to see the counter example of the white belt who came back and had no problems. A purple belt, by contrast, can come back after months of layoff and have lost almost nothing mentally, just physically.
I have no mechanism to explain this, but that has been my observation.[/QUOTE]

Concur. Jiujitsu is very dependent on timing. Timing is dependent on routine practice. I'd bet dollars to doughnuts you can do both at the same time, just picking the particular training day to focus on either discipline and giving priority to one or the other depending on required effort or schedule.