Our gym started training Yurchenko's (timers) with my dd after her Level 6 season. The coach says that it takes about a year to learn the skill and at dd's gym if you compete Level 8 you have to do the Yurchenko.
Good luck and realize it takes a while to get this skill....
I absolutely loved yurchankos! They're fun and pretty easy to learn. We did drills for about two months and then we were successfully flipping them, almost comp ready. Like others have said, it must be a gym rule because level 9's can compete them. Good luck and let us know how they go for you! I personally found them to be easier than Tsuks.
As for the girls optionals, I've seen them compete yurchenko in 8 besides tsuks. However, there are a lot of BAD yurchenkos and tsuks. Good enough so they don't hit the back of their head under the table as they rotate over. Well good enough by a near miss. Personally, I'm of the opinion unless they're GOOD, then you should train them but not compete them vs throwing them. Too many skills get thrown in optionals ( back giants and layouts ). In optionals levels of 8 and 9 you won't seem them really turn over off the table and it get's hairy from there. Ugh.
At first I never liked yurchenko, but I've come to enjoy it more now that they are running full bore into it. I think I will be nostalgic and favor Tsuks and front handspring vaults ( ever see front handspring entry? ). I'm not a fan of Kasamatsu really. I love side summis but they just seem half-arsed.