Is there any way to make Nandroid backups take less time?
Than what? How long do they take now?
If they take you 20 minutes, yes. Many ways.
If they take you 3 minutes, no.
You can try a different recovery. TWRP makes much faster back ups than CWM and it's variants (but there are tradeoffs)
Disable MP5 generation during backups. That will shave 30 seconds off the time. (But with possible consequences...though I never generate MP5's and never have a problem)