How long does a guild control a planet after it has been conquered? Do you control it until the next guild conquered the planet, or for a fixed amount of time?
I just investigated this and it appears that the answer is that you retain control of a planet until either of these occurs:
- You conquer a different planet
- Someone else conquers the planet you control
On The Shadowlands server, Tatooine was conquered by <Old Republic Dads> 2 weeks ago. Last week, they conquered Hoth. I just travelled all around Tatooine and the zone message said "No guild controls this sector" the whole time, illustrating case 1.
Similary, Quesh was conquered by <The Drunk Tanks> 2 weeks ago. However, they did not manage to conquer a planet last week. I headed to Quesh and immediately saw the zone message saying that they controlled the sector, illustrating what happens when neither case is met. Importantly, it shows that you can maintain control of a planet for longer than a week.
I did not confirm case 2 explicitly, but I think it's a safe assumption!
Refer to SWTORConquest.com to see historical Conquest data.