After his wife and childhood dies unexpectedly from an illness, a Marine gains the ability to time travel so that he can remember all the times he spent with her.

If he can timetravel, how is this related to getting memories back? If he does timetravel he'll be physically there.
Does he needs memories or physically be there? Depending on that : timetravel or something else?
And. I guess the ptsd causes loss of memory?
Just my 2 cents :-)

I revised it.

This is not so much for this specific logline but rather your overall logline writing skills, and so here are some important resources to further your understanding of a logline:

• Fast Screenplay ? The Producer's Perspective Part 1
  • https://www.youtube.com/watch?v=r01B6mPXMjU&ab_channel=FASTScreenplay

• Fast Screenplay ? The Producer's Perspective Part 2
  • https://www.youtube.com/watch?v=KJxS4p8ZzZc&t=1s&ab_channel=FASTScreenplay

• The Script Lab ? How to Write a Logline
  • https://www.youtube.com/watch?v=z4a9JRjP86Q&ab_channel=TheScriptLab

• D4Darious ? How to Write Compelling Loglines
  • https://www.youtube.com/watch?v=bvlWd2tz4xg

Watch these videos in order and watch them again and again until you've memorised what loglines are all about. Being vague on what makes a logline puts you at a huge disadvantage up against people who understand what makes a logline.