Every region can have at most two regular missions at the same time and then special ones like liberation missions or Advent activities like the precursor mission for a haven assault.
The time you then have for infiltration is simply what's left before it reaches its expiration date. They already have an expiration date set and need to be revealed via the intel haven job. Mission Generation and Haven ManagementTalking about it, I feel like it's important to outline how mission generation works: Upon contacting a region or when currently present missions expire (either because they reach their expiration date or you went into tactical for them), new ones spawn but are initially hidden.
