Our core hours are 7am - 4pm. Most of us do 7am-3pm with some doing 8am-4pm if it suits their home life (childcare etc...)
Our units all open at 7am so it's good to have techs on the ground ready to go.
We have been asked to cover our units 7am-7pm recently so that is something we're looking into although I'm not a fan for my own personal reasons. We've never had a tech on site after 4pm for 30 years and it seems to have worked fine. On-call takes over from 4pm.
We have one tech in on a Saturday working the same hours.