Minato can last longer. Even Naruto when he was training Sage Mode last more tha a minute. When he fell down to the rocks he coul last longer. But the time is reduce when using a tecnic. Naruto vs Pain could last 5 minutes or 2 Futon Rsen SHURIKEN.
So if you use a tecncic is will reduce your time in Sage Mode. But remember these facts, for sennin mode you need a lot of chakra, and Minato does not have the chakra of Hashirama, he has a lot but not thar much. Remember that he was an Edo, and Edo has there chakra lower, so it is a great feat that Minato Edo can go to Sage Mode, this is meaning that only a smaller amount of Minato reserves of chakra is need for sage mode. So when he is complete he can last longer. Other thing is that he only gather enough natural energy for one tecnic, a rasengan. And i can say this because he threw a Kunai before entering sage mode which means he was moveing before showing us he gather energy between he threw the kunai and use the hiraishin.
So if stays still like Naruto he can last longer