I want to add dsta to my runs, but im not sure how it works. My current pb exits cascade at 6:20 (which is slower than my average I usually exit cascade at a mid 6:1x) What should my offset be?

Anything above 6:05 is basically not possible

If your cascade exits are somewhat consistent, you can do DSTA. with 6:10 exits you would probably want to set the time to 1:52 with a -55 to -50 offset. This is a very long time to wait for a reset so I wouldn't recommend it, but once you get sub-6 cascade exits it's going to be much quicker.