Unfortunately with MATLAB you need to use temporary variables. It doesn't support this kind of indexing, though it is quite natural and I would love if they supported it.
You would have to do this:
x = Time(something==X);
y = x(1);
Octave does have the ability of doing this kind of indexing though. The only way I can think of you escaping this is if you use cell arrays. However, if you want to use a normal vector, then you're SOL.
EDIT: May 13th, 2014 - Referencing David's comment, it is possible to do this without a temporary variable, but readability is very poor. In the end, a temporary variable is still the better way for readability and reproducibility. Check the following SO post that he has referenced: