What Minato does is technically a short cut between point A and b, unlike other people who have to run the full distance from a-b, think of ftg as folding the a-b line in half and walking right through the middle to end up at b
Technically this shouldn't be even considered "speed" , but kishi does, so meh
If you wish to take it in naruto terms, Yes he's faster than the speed of light..
Let's say miniato hypothetically has a ftg tag on the sun, and on one earth, He can essentially instantly move from the sun to earth with no travel time.... Light on the other hand takes about 6mins? or so to reach earth....when you look at the sun, you're basically looking 6mins into the past, When you look at stars, you're sometimes looking thousands of years into the past
In naruto terms, where instantaneous transportation is considered speed, then yes he is faster than the speed of light