And you calculate that time period how?I don't need any validations given the action in the manga. Use a bit of theoretical time calculation. Sheesh ...
Because the user needs to move during combat, the senjutsu chakra cannot be replenished, which means the user can't stay within this state for extended periods of time.
The second and third weaknesses mentioned above can be bypassed through the Sage Art: Amphibian Technique, where one Sage gathers chakra for another or as in Naruto's case, shadow clones can be used for the same purpose.
Sage mode was always short lived unless like Jiraiya you get help from other sages ( frog sages in his case) and for Naruto his kyuubi chakra and kyuubi collecting it for him as well. Ordinary Minato without Kyuubi and without hands to summon anything is not going to able to use SM much. If it's about alive Minato- we can only speculate.
He did showed quite an stamina and chakra level while fighting with Tobi back then and even dying he left enough for emergency back up sealed in Naruto. So if he knew how to use sage mode I doubt it would be that short as to last 5 seconds only. Just not enough to suit his fighting style.