Find below answers
1. We understand that QlikTech would generate license for clustering, what would be the impact on production running on. Will the production go off license if we turn on PoC server 1 and PoC server 2 with a clustered license.
You can run one Licence per environment, Or else your both servers will be down, If you need to run two similar setups. I would suggest you to avail Test Licence that you can use in your QA or POC.
2. It there a time limit within which the cluster license has to be applied.
Every Licence will have time limit, after which you will not be entitled for support, but your Licence will be functional.
3. Is there a that QlikTech provides for performing such tests that does not impact production.
Yes, Qliktech do provides test or trial licences, for this contact Qlik Partner in your region.
Hope it helped.