Gains that arise on the appointment of assets from a trust to a beneficiary can be deferred either under s165 TCGA 1992 (for qualifying business assets) or s260 TCGA 1992 if the transfer to the beneficiary is a chargeable transfer for inheritance tax purposes, irrespective of whether there is actually any tax due to HMRC on the transfer.
Where a trust is considered an 18-25 settlement, then holdover would apply on any appointment post 18. Where a trust is treated as a relevant property settlement, then holdover would apply on an appointment of trust assets to the beneficiaries at any point.
In your scenario, one assumes it is a full relevant property settlement. Holdover would apply at any time assets are appointed to a beneficiary to defer the gains so arising.
Rawlinson & Hunter