Here in "Holy Catholic Ireland" (!), Mass is normally done and dusted in 30/35 minutes on a Sunday, less time still on a weekday.
Mask wearing still in place, a significant proportion of the congregation will be elderly/vulnerable. Use the hand sanitiser provided at entry points.
The Sign of Peace, shaking of hands has not returned since the pandemic, you may be invited to make eye contact with your neighbours and say "Peace be with you".
Dress respectfully, but casually, definitely no need to cover your head but do cover your midriff.
There may be a place assigned for special needs people in the church, in our church there is a place to park wheelchairs and the Ministers of the Eucharist will bring the Communion wafers there. If you arrive early, you can ask the sacristan (caretaker/not quite receptionist type of role). Or, there may be a "meet and greet" volunteer on duty. Most older churches will have steps, the steps with a ramp attached may be at a different entrance. Some churches have a "Crying Room" type of facility - this is a room where you can essentially hear the service but the rest of the congregation won't be able to hear you (or crying babies, upset toddlers etc), depending on the set-up you may be able to see the service through a large glass screen.
Please don't feel obliged to contribute to the collection(s). If a basket is passed, then just pass it on to the next person. However, since Covid, it's more usual to have buckets at the entrance/exit points.
Don't think of it as time wasted. It can be a lovely restful spiritual or meditative experience for you. There may be music. There may be some lovely stained glass or artwork to admire as well as the architecture of the church itself. Enjoy your visit.