I feel like this song is about someone who is reminiscing about their past and wishing they had more time for things, or to fix past mistakes.
The "Time Traveller" in the title, is who's singing the song (could be Chris, or him singing as a sort of "character"). This "Time Traveller" is singing to someone, warning them about his past. I believe this is an older person nearing death, and thinking about his mistakes. He wants to go back and fix what he's done, and he's "curs[ing] the calendar" for "stealing" his time. He's essentially cursing time for going so fast and wishing he had more of it.
I think he's called a "Time Traveller" in the title because he's sort of "time travelling" through his memories, therefore making him a sort of "Time Traveller".
Lyric By Lyric:
"Day by day,
We roll
Into an uncertain future."
Every day, we move forward unsure of what will become of us.
"What our past may hold
Is what constantly embodies my mind."
Constantly thinking about the past fills his mind. (I'm pretty sure he's saying the word "paths" instead of "past" here, but I could be wrong, and that would throw off my entire theory about this song, so I'm just gonna pretend it's "past")
"Wasted time.
Curses to the calendar for stealing
All that was mine."
He's cursing time for being so short and going by so fast, as I mentioned above. "All that was mine" is his time.
"It's time
I finally open my eyes."
He's saying it's time he really thinks about what he's done. As I said before, I think this "Time Traveller" is old and getting close to dying, and he's saying his regrets.
"I don't want
You to see
The past that's deep inside me,"
The "Time Traveller" is hiding his past from loved ones and has kept his secrets very well hidden from everyone.
"And all my love would bring
Is a pathway to the mystery."
This one sort of contradicts what I said before, how he's an older person and talking to a loved one(s). Maybe he's saying that in the past, his love was always surrounded in mystery and he never found love because he figured everyone would hate him the way he is, and just kept to himself.
"All this wasted time,
Curses to the calendar for stealing
All that was mine.
It's time
I finally open my eyes."
The "Time Traveller" is saying once again that he wishes he had more time to fix his mistakes or take them back, or maybe take action to do something instead of sitting around keeping his past inside of him. Notice Chris sings this with more emphasis, like the "Time Traveller" is regretting wasting time even more.
"Curiosity killed the cat."
My best guess for this one is that the "Time Traveller" is thinking too hard about what he could have done (being "curious"), instead of accepting it, and he died unhappy because he was unwilling to accept his past and move forward.
To be honest, I have absolutely no idea what this line really means. I've listened to this song 3 or 4 times in a row now, and I still think that's what that means.
Another theory I have for this song is that this is a middle-aged person singing about how they're finally going to move on from their mistakes, and that they're saying curiosity about what could have happened would just end up killing them in the end, and that they just need to move on.
I hope that all makes sense. XD