Two recent datapoints:

Yesterday started chat at 12.02. Showed 99+ ahead of me. About 15 mins before I got below 99 then moved quite quickly (compared to last time I did it) to about 30 and then 30 to getting an agent in a few seconds which threw me at bit, at 12.51. Started by wanting to get refunds for two cancelled flights, agent was slow but we got the the first done eventually, then he disappeared when we got onto the second and when I asked if he was still there, someone else answered. She did the second refund and then refused to help with rebooking on another airline for a cancelled flight. Finally finished at 2.11.

Today started chat at 8 on the dot. Got through immediately and the agent cancelled another flight for me quickly and without issue.

I'd recommend trying at 8am.