When you stretch can matter almost as much as how you stretch. General guidance on stretching and exercise draws a fairly clear line between what tends to work well before activity and what tends to work well after it.
The General Guidance on Timing
According to Mayo Clinic, muscles should generally be warmed up with light activity before deep stretching, and pre-activity stretching of cold muscles may temporarily reduce strength and performance rather than helping it.
Before You Play or Work Out
The common recommendation is to prioritize light movement — a short warmup that gradually increases in intensity — rather than a long, deep stretching session right before you tee off. Save the more intensive assisted stretching for afterward, or for a separate day entirely.
After You Play or Work Out
This is generally considered the more effective window for deeper stretching, including assisted stretching, because the muscles are already warm. It's also simply the most common and comfortable time for a full session.
On Rest Days
Assisted stretching on a day you're not playing or exercising is generally fine at any point — there's no cold-muscle concern the way there can be right before intense activity.
General guidance favors light movement before you play, and deeper stretching — assisted or on your own — after.