How long does it take to upgrade from tier 3 to tier 5 clearance?

That's a pretty open ended question. How backed up is OPM? How long since your last investigation? Were there any flags that needed to be investigated and how severe? How backed up is OPM?

Even your security manager can't tell you exactly how long it will be on any given day. I've seen it take anywhere from six weeks to a year. I'd say most of the time time it falls between 3-9 months, but even that mostly depends on how backed up is OPM at the moment. I haven't sent anyone for an upgrade in well over a year, it might be quick right now

Upgrading from a tier 3 to a tier 5 clearance can be a frustrating waiting game. It's understandable that you wouldn't want to leave your current job until the new one is a sure thing. While the HR department might not have specifics, it might be worth talking to the new employer's security team directly. They can likely give you a better idea of current processing times and if you might be eligible for an interim clearance while the full investigation for tier 5 is ongoing. An interim clearance would allow you to start working on classified https://www.linkedin.com/pulse/4-best-coursework-writing-services-uk-students-mary-walton-y0ome information at the Top Secret level even while the final clearance is being adjudicated.

Are you changing agencies. If not your Personnel office should leave your in your current position (if that position is not being eliminated) until you are qualified (to include security clearance) with your new position.