If it's a good crossing Texel, there's no reason your Mule x lambs won't finish in a season. But depending on where you are, and when ovine hormones start to flow...
BH used to say the thing about entires growing faster than castrates too. But now we castrate some and cannot verify that idea.
In fact, any that are still here when the hormones start do *much* better if castrated - tup lambs seem to stop growing when the hormones kick in
We castrate by ringing at 24-72 hours, or some that we couldn't catch
at up to a week. In terms of recovery time, the earlier the better. I rarely have any still struggling after 30 minutes; I had one flaked out for two hours a few weeks back and I was very worried. (He was fine, of course, just took him longer than most.)
The only thing I'd say agin castrating is that a tup lamb can eat more cake and not slab on the fat than a wether. But since we find that they grow at the same rate, it could suggest that actually the wethers need *less* cake to finish...
The other factor I observe is this.
Tup lambs, or wether lambs, that finish before August are sent when ready. We get good (great) grades and good deadweights. Once we're in August, he sends anything with testicles on that's fat enough. We still get fabulous grades - but the deadweight average drops as we start to send smaller tup lambs. If those lambs had been castrated, we'd have kept them an extra month and got another kilo on them