The timer is linked to when the previous invasion cycle ends. So if someone invades....and either wipes the team quickly...or dies quickly....then their cooldown timer will start well before that of someone who comes over and hides..... ....or takes up most of the 30 second invasion window. Its why Invasion can turn into a really nasty, really maddening STOMP/snowball mechanic. You get invaded.....you get wiped by a really good PVP player. Then by the time your team has respawned, and regrouped.....the cooldown is over...and you're getting invaded again. Rinse and Repeat. So during the mote banking phase, you can get absolutely steamrolled. Having almost no motes backed while the other team is summoning their boss...... ....or during the Boss fight, you can feel like you under almost one continuous invasion.