Spacetime A could be
or in words: The set of all points in 3 dimensions, at any given time, in multiversal position 1 (i.e. 1 is the position in the 5th dimension).
Spacetime B could be
or in words: The set of all points in 3 dimensions, at any given, in multiversal position 2.
These universes are spatially separate. In fact, they are even spatiotemporally separate. There is not a single point in space and time that is simultaneously in A and B. Why is there no such point? Because all points in A have 1 as the fifth coordinate and all points in B have 2 as the fifth coordinate. Being in both would mean to have 1 and 2 as 5th coordinate simultaneously, which is impossible.
And how many dimensions of time have we used? Only one. In our notion only the 4th dimension, which's variable we have used t for, is timelike. The variables x, y and z are the ones for our usual 3 spatial dimensions and the 5th one, that is 1 for A and 2 for B, is the spatial position in the multiverse. Only that one dimension is time. Two spatiotemporally separated timelines, yet only one dimension of time.