I wet bun my hair like this whenever I feel like it and have never had issues. Follow Kewlkat's advice - I'll also add, since ur doing a sock bun, to remember to tuck the ends gently and not pin them since they will be wet. HTH
Thanks ladies for the answers. I decided to just not wash last night. I'll wash today after my interview and airdry and bun. My bun came out pretty good. I have like 5 packs of brand new braid hair that I've had for like 3 years and I cut some and braided it and pinned it around the base of my bun. It's looking cute.