How am I supposed to know when to use an ult in Nexus Blitz?

For some reason the timer is only giving me around 30 seconds notice of an event. But, I know Riot wouldn't be so terrible as to only give me 30 seconds notice on their own because then that would deterministicly dictate the victory to whichever team coincidentally happened to have had the lowest cooldown ultimates or happened to have them refresh just in time for the event; Riot would never make such a careless mistake that fundamentally ruins the entire game mode. So how do I fix the event timer to give me the more advanced notice that Riot clearly intended?