Three independent copies at three different intervals.

r u concerned only about the intervals? or you need to three indepdent copies.?

I would recommend GNS to keep the DGs syncronzied among multiple hosts.

you could put them all in one group but give them different name. For example name one set SET1VDEV0, SET1VDEV1 ..etc and then name devices for second set SET2VDEV0, SET2VDEV1 ..etc, and the same thing with third set. In your script you will need to reference each and every source and target, for example for set 1 you would run:

symsnap -g DGNAME create DEV001 VDEV ld SET1VDEV0

..and so on. If you need to query all devices in the group you can run symsnap -g DGNAME query -multi.

I agree with Santhosh: GNS is definitly the way to manage DGs from different hosts.
And I agree with Dynamox .. you can throw everything in a single DG (3 VDEV for every STD device) and use big command lines (you have to specify every time STD/VDEV pairs).
Or you can use different DGs and have the same STD in different DGs. Every DG have its own VDEVs. Right now (with S.E. 6.X) you have to use strange and unintuitive options (-concurrent if I remember) .. And you need to tweak "options" file to be able to put same STD in 3 different DGs .. But it works.

Have fun!!

-s-