It’s measurement of distance in a set time frame. One year.
It's not time. It's a set distance that uses the measure at which photons travel, which is too long to write in kilometers, so they use "light years" which represent the number of kilometers a photon travels in a set amount of time.
It's purely distance. To calculate time, you need to know the amount of distance and speed.
Saying it represents time would make it the same for a km. You're still missing your measures to calculate time.
Speed of light is somewhere around 300000 km/s.
Calculate 300000×60(s)×60(m)×24(h)×365(d) and that's the total distance represented by a lightyear.
Hence, when we say travel 1 light year, it represents that total distance a photon would travel in a year, which is a set amount, hence a distance.