How long will it take to get a TS Interim Clearance once all paperwork is completed?

Interims should be granted locally. Unless something has changed in the last few years since I was in an S2 shop, the interim was locally granted and temporary. The adjudication was done by OPM (which I know that was removed from OPM after the massive breaches).

In my experience with them, the Security Office granted interims based on the SF86, credit and background checks. An interim clearance denial did not mean your final clearance would be denied and I did see people get a final even after an interim was denied. Interims are temporary so that someone can start to do a job while waiting on the adjudication. The adjudication is what can take months and depends on the individual's record.

An interim should not take months since the purpose of it is to temporarily allow someone to work until the investigation is done.

You'll only nerd an interim to go to school, but even that can take 6-9 months.

It depends of the complexity of the individual’s background.