That is SPECIFICALLY why Valve never tells you the specific amount of time Chell was in stasis.
This could be during the events of HL2 (unlikely given the timeline, but still) and just not in a Combine infested area. It could be just after, and Mr. Freechman hath saved the world. Or even past the age of humans, and earth is just one massive nature reserve.
Either way, I think Portal works best as it's own separate entity, with only a few jokes and references to connect it to Half-Life.
This could be during the events of HL2 (unlikely given the timeline, but still) and just not in a Combine infested area. It could be just after, and Mr. Freechman hath saved the world. Or even past the age of humans, and earth is just one massive nature reserve.
Either way, I think Portal works best as it's own separate entity, with only a few jokes and references to connect it to Half-Life.