It will need at least a decade for quantum resistant algorithms be considered seriously or even make their way into bitcoin. Right now we have no reason to want to think about any kind of fork whatsoever.
We need a similar amount of time for commercially viable,
portable quantum computers to make their way into the market too. We need actual speed benchmarks on how faster they are compared to ASICs, so that people's hard work doesn't get undone by low speed (and hence security) assumptions.