Pretty Please Help - Tumblr Posts

Hey, beta readers and writers of tumblr, I have a question

How long does it take to beta read a thing? Approximately 13 000 words one-shot (dpxdc gen fanfic)(haven't finished it, so I'm low-key guessing it may grow a bit). I'm curious because I wanted to post my next work on a specific date, and I wanted to make it special and had it checked by an actual person and not Grammarly, and I need to know if I have time for it, hah

Also, if someone would be interested in beta reading it, I'll platonically kiss you (or hug, or like, draw something for you, I'm flexible in a ways of showing gratitude)