I'm a maternity nurse and most of the mums I work with chose to express. This is the plan I use:
First feed of the day baby feeds one side and other side is expressed either before or after the baby feeding. If baby is still hungry then they go onto the side that has been expressed.
Second feed of the day alternate what happened with first feed.
I never get the mums to go over 15 mins of expressing and if they are in pain or the milk stops flowing then they stop sooner. I also get them to do compressions and relax as much as possible. Sometimes it is only a small amount to begin with but will build up. Doing the two morning expressing is usually enough for more than one feed, so we freeze the excess.
Most of the mothers I work with then use the EBM in the late evening so I will get them to express then as well. Eg I usually give the EBM between 10-11pm and get the mum to express both sides at 9.30pm then she can go to sleep until the babies middle of night feed.
Sometimes the mums have chosen for me to do middle of night feed so I usually recommend that they set an alarm and express both sides at 3amish until 6 weeks and then can start stopping.
Or I have mums that give a top up or full feed of EBM at the bedtime feed in which case they will express around 7pmish.
I think the key is to relax and take it slowly, the mums I've worked with have had good results with the swing but make sure all the connections are snug so you get good suction.