My own technique is to set some targets for each cycle of training, work to them, and see how knackered I feel. When I'm on the brink of feeling like I'm seriously overdoing it, then I know what to set weekly TSS at, and CTL will just end up where it ends up. If time's really short you'll probably find it's self-limiting anyway and you'd be better off just focusing on putting as many hours as possible into the sort of training that most suits your race/event aims.