Full Idea
Time is a necessary representation that grounds all intuitions. In regard to appearances in general on cannot remove time, though one can very well take the appearances away from time. Time is therefore given a priori.
Gist of Idea
One can never imagine appearances without time, so it is given a priori
Source
Immanuel Kant (Critique of Pure Reason [1781], B046/A31)
Book Reference
Kant,Immanuel: 'Critique of Pure Reason', ed/tr. Guyer,P /Wood,A W [CUO 1998], p.162
A Reaction
As with space, the notion that time is a purely a priori intuition, and not a real feature of the 'space-time manifold' strikes me as absurd (though, unlike space, a reductive account of time might be possible), but its absence is indeed unimaginable.