Some maps have helicopters, boats, etc. that spawn at an objective. I have a few questions about how the spawn timer works in general. Do the vehicles spawn slower than they do in base? Does each team have it's own separate timer that pauses when they lose the objective?
I believe it's just a timer for when the vehicle was destroyed, independent of what team controls the objective.
Here's a list of server defaults, and there are vehicle spawn delay table on Page 2 https://drive.google.com/file/d/0B8g9NtK6bcjMWjVITnZqVDZmc2c/view