The trust store seems to contain certificates, but that's an illusion (or a tradition). Technically, a trust anchor, i.e. the basis for the trust in certificate validation, is a name coupled with a public key. It so happens that people found it convenient to store the name and public key as a file with the same format as a certificate; this required some trickeries, such as the "self-signature", which makes no sense but had to be included because the format for a certificate includes a non-optional field for a signature.
At that point, it really depends on the OS/browser internal conventions. Some implementations will look at the "validity dates" in the trust anchor "certificate" and will use them as, indeed, validity dates (i.e. beyond the end of validity date, they will cease to trust that trust anchor, even if it is still "there", in the dedicated store for trust anchors). Some other implementations will ignore these dates altogether. It is really up to each implementation to make these choices, since the standard is silent on the subject.
So you have to test.