By 'downtime' I mean nice easy things, like online shopping, coffee breaks, and a bit of random internet surfing.
I work full time and have a 90 minute standing/rushed commute.
Mornings are a rush with early start and nursery drop off etc, My DH picks up DC from nursery between 6 and 6.30 pm, and i reach home about 7pm, spend an hour doing bath, bedtime routine with DC while my husband cooks, we eat at 8.30 then its cleaning kitchen, laundry and general housework, and getting sorted for next day while my DH catches up on work emails. Weekends are also quite jam packed as both our families live far away, so more often than not we either are travelling 300 miles (at least once/twice a month), or family/friends are staying with us.
So I don't get any 'free time' at home, hence i feel i need to take some 'down time' at work. My workload isn't always 100% capacity, but its the type of job where i need to be there and available or it impacts the team. Its paid well and often things kick off i do need to work late into the evening, and sometimes at weekends from home. (I don't get paid for this 'overtime', which is how i justify to myself that the downtime at quieter times during the day is ok).