My guess with minimal knowledge in the field is, weeks if they have a shut down FBR plant, months if they have a decommed FBR Plant. I feel like building a new one to 'ramp up' would either require more time or perhaps multiple smaller reactor projects working in parallel might do the job...
In all honesty, it feels like everyone's arming for something big - from UAE all the way to the US and China, every country is in the process of buying startups and firms working on dual use technology.
Every country seems to have some sort of a 5-10 year roadmap to modernize defense technology and logistics by 2035, yet I never saw this level of concentrated effort globally after 1989.
[0] - https://asia.nikkei.com/Business/Energy/Japan-nuclear-resear...
That said, I sincerely hope my prediction is just paranoia and that I'm wrong.
It's UAE and Saudi's deal flow that got me worried recently. I'm seeing those guys everywhere in the defense tech space now, and if Saudi and UAE are stockpiling, then every other semi-competent regional power is as well.
https://www.bbc.com/news/world-middle-east-24823846
https://en.wikipedia.org/wiki/Saudi_Arabia_and_weapons_of_ma...
Imran Khan leaned pro-Qatar, which irked KSA, especially because IK turned down joining Saudi's coalition in Yemen.
It was around this time that KSA began charting it's own independent course, just like UAE.