Tile Adhesive with UF Heating

Am about to start tiling floors in new build that has underfloor heating (not yet running). A tile shop has advised that once tiles have been laid, the underfloor heating system can't be turned on for 28 days afterwards. This seems a very long time.

Does anyone know if this is correct? If so can you get a rapid setting adhesive that allows the UF heating to be turned on a shorted period after tiles being laid?

Hi,
We have UFH and tiler told us to reduce the flow temp and slowly increase it over a period of a week or so.
But if you're getting tiling done now during summer (ha ! what summer) you probably won't have to worry if you don't need to run UFH.