How long do O-Shot effects last?

The mistake here is asking for a duration before asking whether there is a proven effect to last. A number sounds like an answer. It is only worth anything if research stands behind it.
No proven duration to quote
www.healthline.com says: "There’s currently very little research on the O-Shot, and no scientifically proven evidence that it can improve your sex life."
With that little research, there is no dependable number of months anyone can quote you.
Ask where a quoted duration comes from
When a provider or an advertisement gives you a duration, ask what it is based on. A figure from a clinic's own patients is a different thing from a figure that comes from a study.
Do not read this as a claim that the treatment does nothing. The source says the proof is missing, not that the result has been checked and found absent. The honest position is to hold the question open.
Do not prepay for a promised timeline
Do not pay for a series of injections on the strength of a promised timeline. Ask the provider to put in writing what is known and what is not, and take that document home before you decide.
If your goal is better pelvic floor function, MedlinePlus on pelvic support problems lays out the wider topic. For the treatment itself, see the Healthline explainer on the O-Shot and PRP and the Scary Mommy article on the procedure.
A duration without research behind it
A promised duration with no research behind it is a sales figure. Treat it that way.