Working from Southeast Asia with a UK time-zone 9-5

Thinking about going to Vietnam for just over three weeks and working remotely from there a bit to save on annual leave. My job is UK 9-5, however there is flexibility in that you can finish at 4pm if you want. I’m thinking of going for just over 20 days but my goal is to use only 11 days of annual leave (the flight would be in the afternoon so day of travel required no leave and there is a bank holiday around the time I want to go) – so likely looking at doing 5 days remote. Has anyone done anything similar and what was it like?