Dave

Whitestar is a tub dispersion adhesive and will take a lot longer to dry than a powdered cement based adhesive.....as for levelling over the tilesafe membrane then you should have allowed the height in the installation to compensate for the extra height of the leveller over the ufh....I ahven't used the tilesafe as of yet.....here is some installation advice from tilesafe.....but you can also contact wetdec as he sells them systems and he will talk you through it......

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Application of Tilesafe MembranePrior to the application of each length of Tilesafe Membrane, remove the plastic film from the underlying Tilesafe Reinforcing Tape.
Apply pre-cut lengths of Tilesafe Membrane to walls first, applying as vertical drops and terminating at the floor/wall junction (overlapping the reinforcing tape by 75 mm).
Tilesafe Membrane should be butt jointed rather than overlapped. All butt joints in the membrane should be positioned over the previously applied reinforcing tape, ensuring a gap of 2-3 mm is maintained which should be subsequently filled by the Tilesafe jointing compound. Continue in the same manner for floors, cutting membrane around any pipe entries, taking care not to damage the reinforcing tape below.

Application of Jointing Compound
Using an applicator gun, apply Tilesafe Jointing Compound at butt joints, pipe entries and at all wall to wall and wall to floor interfaces.
The compound should be gunned in to the previously formed 2-3 mm channels, which should be fully filled.
Tooling can be carried out with a profiling tool within approximately 10 minutes of application.
Allow Tilesafe Jointing Compound to cure overnight before applying tile adhesive.
The membrane surface and joints should be thoroughly inspected prior to tiling. Particular attention should be paid to the pipe entries, ensuring seals have not been damaged by following trades between application and tiling. If necessary a re-application of Tilesafe Jointing Compound can be made.
The plastic release film is left in place until immediately prior to tiling.

Application of Tile Adhesive and Tiles

Prior to application of the tile adhesive, which must be rapid-set, flexible and waterproof, the plastic backing film must be removed.
Application of tiles to Tilesafe is essentially the same as normal tiling. There are a few points to consider to ensure satisfactory application:

• If a batten is to be used for tile alignment, this should be secured to the wall through the backing release film, not after this has been removed.
  
• Remove the release film only from those areas where tile adhesive is to be immediately placed.
  
• Leave the backing film in place on the floor areas of Tilesafe while tiling the walls.
  
• Silicone sealant will react with Tilesafe. If silicone sealant is to be used, for example on bath surrounds, ensure it does not come into direct contact with the Tilesafe.
  
• In the unlikely event of the Tilesafe Membrane being damaged, it is easily repaired by applying a piece of reinforcing tape over the damaged area, ensuring a minimum overlap of 50 mm.

Good luck...