i share your enthusiasm for time travel in general & in movies. Underseen is tricky, there's been a lot of talk about Predestination, Primer & Timecrimes recently so they may not be as underseen as i thought. They're all great tho. Gym mentioned Sound of my Voice which is a fairly original and interesting take on time travel.

Here's some

Time After Time 1979 - comedy where Malcolm McDowell as HG Wells hunts David Warner's Jack the Ripper through time.
Triangle 2009 storm hits boat, wierd stuff goes down
Twelve Monkeys 1995 maybe too popular
Red Dawerf 1988 TV Series with plenty of time travel related eps
Bill & Ted movies again popular but worth mentioning
Time Lapse 2014 a camera that takes pics 24hours into the future. what would you do with it?
Paradox 2016 Zoe Bell n her scientist mates send someone an hour into the future, turns out to be a shit idea
Waxwork I & II some may not have seen these. doubt it, but hey
Slaughterhouse Five 1972 a war veteran becomes unstuck in time
Blackadder Back & Forth 1999 one off TV special Blacky n Balders test out thier time machine
Trancers 1984 Box brought me to this franchise & Jack Deth!

and i have to give a shout to Hellraiser iv Bloodlines an absolute shamble but a fun one

Inferno is my favourite of the sequels post part II. I have a soft spot for the entire franchise, inc books, art, comics etc so my judgement of the films is skewed by this predisposition. plus it has The Sheff who has a Barker connection with Nightbreed.

most, if not all the direct to video sequels of the 2000s were stand alone scripts adapted to the Hellraiser franchise. the last one was made simply so the studio could keep the rights. there's a new one out this year (supposedly), same director as Revelations so im expecting the same type of dross but im still gonna go see it coz im a mug like that.

enjoyed that, nice one for posting