How can I keep time out of combat?

How can I keep time out of combat? I’m currently running Tomb of Annihilation (ToA) and I know later in the adventure I’ll need a way to keep track of how long the party has been exploring (this is for in the tomb itself).

Last time I played this as a player our DM didn’t have much of a way of keeping time which led to us (admittedly more me than the other player) constantly asking if it had been long enough for the party to take another long rest. This became even worse when my Warlock opted to not rest with the rest of the party before what she suspected was a big fight for the sake of not losing her 17 temp HP.

I’m hoping to avoid situations like the party asking when they can take another long rest by having some standardized way of keeping track of time when not in combat in a way the players can also keep track of. I thought about simply keeping initiative the whole time but that would be a highly impractical option considering that would be 14,400 rounds by which time they could explore the entire dungeon most likely.