If your novel is in third person POV past tense, would it be negatively impacted if you read novels in a different POV during the months you are writing your novel?

Reading novels written in first person shouldn’t impact your novel. If anything it will show you the limits of first-person. I believe it helps to read novels in different POVs and tenses. Just because you’re writing in one POV doesn’t mean you’ll absolutely switch from third to first, then again you might decide that your novel will read better in first.

If it turns out that section(s) (hopefully small ones) have a POV or tense switch you can rewrite those section(s) especially if you’re working on your first draft.