If you're talking about the same workbook then the only option is to speed up the query (subset of data / use an extract / etc) while you're developing.
If you want to switch to a different workbook, that is doable by starting 2 instances of Tableau.
I think you're meaning the first option though, so you need to speed up the time for the query to execute.
No, don't start multiple instances of the same workbook - that's never a good idea.
What I mean is - if Workbook A is refreshing (and taking a long time and you can't speed it up more), the only option you have is to work on Workbook B (ie another different workbook)