You need to visit each base to refresh the decay timer. If you have not built a base as one connected piece it is likely you will need to go close to each separate structure to refresh the individual segments.
Note you might have to stand near them for a minute or more before the game recognises you are in proximity to refresh the timer … I tend to carry a repair hammer and equip that to confirm the building decay has reset (I recently learned you can press Tab whilst looking at a building piece and that will also allow you to see the decay time.)
Some people have built their bases by connecting them with a continuous line of foundations or ceiling tiles and then later deleted those connections - they say that then the buildings then share the same decay time reset and they don’t have to visit each place … but to me that sounds unintentional on the part of the development team so I’d not rely on it.
I just add this tip: if you play on PC and you don’t had remapped buttons you can also hold the TAB button to see decay timers even without using a repair hammer