Yes, the initial distribution was for a longer period. Nevertheless both SDT and PER will probably be pretty good investments PROVIDED THAT the parent SD stays financially healthy.
The S-1 for both trusts included a big table of projected distributions going out 20 years to the end of the trust life. You can probably still find it on edgar. SDT is one quarter ahead of PER and is so far running well ahead of the target distribution in the S-1 (as is the case with the initial PER distribution).
I think both of these are going to be good investments (with the above proviso about SD) and maximizing total return implies getting in as soon as possible (to capture as many distributions as you can).
ps. grannybones is a spammer posting the same thing on dozens of boards.