Choose whether or not to run extra missions in that region accordingly. This will make it harder to complete both Lib 2 and Lib 3. Running lot’s of missions in a region in a short period of time, will increase Advent Vigilance, and with it Advent Strength in that region. Region Vigilance is hidden unless you install certain mods. And if you pursue many of them, this can present a different problem Spiking Advent Vigilance. With all this scanning for Lib 2 you will usually end up finding many other missions in the region. As soon as it expires it will immediately respawn.
And to boost it you will need some Intel (30 at Legend difficulty) If the mission appears with 3 or less days, don’t stress. To make this happen, you will need to put all your personnel on Intel, even if you have 13 guys in your haven. Your goal should be to get enough time (5+ days), that with an Intel boost you can send a full team (6+ soldiers). Lib 2 and Lib 3 are super hard to detect. The second mission is much harder to stealth, and so you will want more time to infiltrate a full team. So Intel gathering is only important for the first 3 steps to Liberation.
Once you have completed Lib 3, The Network Tower is automatically available and will not expire. This will give you more time to infiltrate on those missions, which is particularly important for Lib 3, which can be very difficult. Don’t worry about the mechanics too much, just know that you will want more Resistance Personnel in regions you intend to liberate, and you will want to put them all on Intel while trying to find Lib 2 and Lib 3. So you can always find them… But they are incredibly hard to find, requiring a larger pool of intel to be collected, and then a harder luck roll to find them. The minute a liberation mission expires, it immediately respawns. Excepting that one circumstance, a Liberation mission is always, ALWAYS, available in each and every region you have contacted. On Legend difficulty, Liberation missions are not available until the 2nd month of the campaign.