Hey!
Congratulations on the VS offer!!
In general, I don't think it makes any meaningful difference to your chances whether you attend the first or second scheme week. The firm will have the same criteria, structure, and standards across all of the cohorts, and the graduate recruitment team are aware that availability varies.
I'm conscious that some people worry that the earlier week has an advantage because it is first, or the later week will have less TC spaces, but in practice firm's don't operate on a strict first-come-first-served basis fro training contracts. They'll usually review candidates across both the schemes before making final decisions, so you aren't disadvantaged by attending one week over the other. Plenty of firms won't have a set amount of TCs to hand out either, and will often make offers to any candidates that meet their benchmark.
What matters far more is your performance on the scheme itself - for example, how you engage with the firm, the quality of your work, and how you interact with your team. Therefore, I would choose the week that works the best for you and where you will be able to perform at your best.
Wishing you (+ all those that received
SPB offers today) the best of luck - I'm sure you will smash it!!