Hi,
I was employed as an ATCA at LATCC when the IBM 9020D was introduced as a replacement for 'Hermes'. The date must have been late 1974 or very early 1975 as I left to go to Gatwick in April 1975.
9020 was the same animal as one used in the USA, although I believe our American comrades were in the process of throwing theirs away.
Every night it was shut down at around 2300 and things reverted to manual throughout the quiet period. Restart was planned for around 0600 but rarely made it on time as it frequently had the sulks. This was mainly due to the entire night being taken up with 'systems testing', including what sounded like destructive testing. Around 0200 the whole Op's room would be woken by the sound of every terminal and printer running flat out for about 30 minutes. If nothing broke then it was declared fit for the next day. Things nearly always did break! IBM declared that it was rather like driving your car down a motorway at 60 mph then slamming it into reverse to see what would happen!!
After a couple of years I think it was considered wiser to leave it switched on 24/7 and not tempt fate.
Regards
Slightly Mad