Book craftsmen as early as possible. They don't need finished walls for an offer. Of course, the price might change if the walls turn out to be worse than expected. Book tilers also as soon as possible. You search for a while, especially if you don't want to pay exorbitant prices. We recently looked for one, for months, many quoted prices beyond reason. Prices must always be fair for both sides in my opinion. Ultimately, they know that a construction site is hardly predictable. Especially painters and tilers, who are always among the last ones. Just reach out. Communicate openly that you only have a rough idea of the timeframe but will inform them as early as possible. I told our tiler in advance it would be approximately June or July (that was around March) and we agreed that I would let him know as soon as the screed was foreseeable. Then again when the screed was laid and then with the heating protocol – then we were fixed in the schedule.