There is no requirement for differences training in TMG. SEP, SET or MEP aeroplanes to be completed within a DTO/ATO unless the manufacturer requires it in the OSD-FC.
FCL.710 Class and Type Ratings - Variants
(b) The differences training shall be conducted at any of the following:
(1) an ATO;
(2) a DTO in the case of aircraft referred to in points (a)(1)(c) and (a)(2)(c) of point DTO.GEN.110 of Annex VIII;
(3) an AOC holder having an approved differences training programme for the relevant class or type.
(c) Notwithstanding the requirement in point (b), differences training for TMG, single-engine piston (SEP), single- engine turbine (SET) and multi-engine piston (MEP) aeroplanes may be conducted by an appropriately qualified instructor unless otherwise provided in the OSD.