Pavel,
I almost don't want to post this here, as I am aware that you are FAR further along the path than me (just toying with 32), but I thought that there was a possibility it could help, so here goes:
Have you tried doing 4 (or so) rounds of Wim Hof breathing before your Sinister timed practice?
I ask because, for me, this was a game changer and cut my rest between sets by more than a third. I know, from your excellent log (Thankyou) that the time between swings and get ups is the last obstacle between you and timed sinister, and we are all rooting for you, so just wanted to ask (from the point of view of an S&S white belt.)
Thankyou for all you do, it is inspirational.
Be well.