I have twins who share a room as well. I have read your other responses and while I agree with some of their responses, I don't think they really deal with what is going on here.
1) Yes, the time change does have an effect on your child's bedtime routine. While you are able to adjust, your 20 month old twins have no idea, and their internal clocks certainly do not understand the concept of leaping forward and falling back twice a year... So, until they are a few years older, when our clocks change, they will take a week or two to adjust...
2) As far as them getting up and playing when you put them to bed. This is much like when the began climbing out of their crib. You put them into toddler beds so that they wouldn't fall trying to climb out of the crib and hurt themselves. But now they have discovered "hey, we can get up all by ourselves!!!" so they do.
In order to resolve this all you need is consistency. With one child it usually only takes 3 or 4 nights and naps, but because there are twins who feed off each other being in the same room it will take a bit longer to sing in, you may be in for one to two weeks, but if you are consistent, the following will pay off, I promise.
When you put them down for a nap/bed time you tell them to stay in bed and go to sleep. As soon as you hear signs of them getting up, you go in and put them firmly back to bed and tell them no it is nap/bed time and they need to get their rest, stay in bed and go to sleep.
At nap time keep it up until they either go to sleep or have been there as long as their nap time usually is. At bed time keep it up until they go to sleep. It is tiring and frustrating, but it WILL pay off, and your kids will go back to their normal routine.
I would also suggest making sure they do something that uses up their energy close to time for nap or bedtime whether it is a running free out back or coordinated excercises with mom or playing something like simon says or redlight/green light (which are great, by the way, for teaching them to listen for specific signals from you or others, or to stop on command).
Good Luck...and remember, this too shall pass, and your girls will give you hugs and kisses and you will forget all about how tough the bed time thing was!!! ;-)