Philip Hammond has given the clearest indication of the government's hope for what it means by a transitional period.
During a grilling from the Lords, the chancellor said the hope was that the period after March 2019 would be "similar" to being in the customs union - but with the added bonus that trade deals could be negotiated and signed, ready for implementation once the period ends.
Asked whether businesses would be able to import and export without restriction during this period, Hammond said that would be the case on an interim basis.
Asked if he thought the EU would accept that he said the bloc was "clearly contemplating" this kind of arrangement.
When it came to trade Hammond, who also revealed the Budget was set for 22 November, said "the design challenge is to minimise the friction to a level that is acceptable to business".
During David Davis' recent visit to the US, the Brexit secretary observed customs arrangements at the border with Canada, where the typical delay was a minute - or half that if traders used a trusted trader system.
The Sweden-Norway border was also of great interest, as it is an example of a border between the EU and a non-EU country.