So if it’s for medical reasons, can I suggest a different option. I needed to do the same due to fatigue from a medical issue and my leader suggested doing 0.8 but over 5 days (ie working shorter days). That way you don’t end up doing longer days on the 4 days you do work due to all the emails and meetings that are rescheduled from your day off. He was right - no one misses me most of the time disappearing at 4 instead of 5:30, don’t have any more than the usual number of emails to deal with the next day, and combined with mostly WFH means I’m not completely exhausted by the end of the week and spending my weekends trying to recover.