"There needs to be something which allows us to control how long we are there for to avoid any sense that we are left indefinitely in a sort of customs union limbo," he told the BBC. "That wouldn't be acceptable."
Raab added: "It would be rather odd if we ended up in that bridging temporary mechanism without a route out, so it could be time-limited, there could be another mechanism."
The comments came as Prime Minister Theresa May faces a furious backlash in Britain after indicating at an EU summit last week that she could accept a longer post-Brexit implementation phase than previously envisaged.
The shift aims to break an impasse in negotiations between London and Brussels over how to keep the Irish border open after Brexit, by giving the two sides more time to agree their future relationship.
But it angered Brexiteer colleagues in May's ruling Conservative party who fear remaining tied to the EU for years after Britain's formal departure next March.
Several Sunday newspapers said mutinous MPs were preparing a fresh bid to topple her leadership this week.
Amid the fevered talk, Raab also argued Sunday that an extended transition period would be "an alternative" to a so-called backstop agreement to keep either Northern Ireland or all of Britain in a customs union should the future trade talks end in deadlock.
Writing in The Daily Telegraph, he said May was "considering different approaches" to kickstarting the stalled talks but she "won't sacrifice Northern Ireland".
"The prime minister has rightly refused to rule out considering different approaches –- including extending the implementation period for a limited period of a few months, as an alternative to the backstop," Raab wrote.
But EU leaders, who see the backstop as essential should talks over the future relationship falter, are unlikely to welcome the stance.
France's Europe minister Nathalie Loiseau told the BBC Sunday that the bloc needs "definitive answers, or at least no temporary measures which disappear and we don't know what to do after".
Eyewitness? Submit your stories now via social or:
Email: eyewitness@pulse.ng
