In all the three major Japanese leagues, time limit is 5 hours per player. However I'm not quite sure what is written where it explains the overtime . . . https://www.nihonkiin.or.jp/match/meijin/048.html

The Honinbo had 8 places and 4 of them where from qualifying through a preliminary tournament. The Meijin has 9 places but only 3 places are gained through qualification!? Well this is changing next year since the number of seeds in the Meijin will decrease from 6 to 5. Are we witnessing the end of history for real this time?

It will be difficult to wait past the middle of next year for the tournament bracket for the final qualifier of the 49th Meijin

Mysteries of such great magnitude are best left to detective Mickey Mouse but with duckchess being all the rage in Duckburg there is little hope for help from mr. Mouse.

I'm guessing you are unsure because you are inadvertently using the word 'overtime'.

The Japanese system in major title matches is to give the players a time allowance (say 5h each in the Honinbo League) and to say that the last N minutes (last 5 in this case) are to be used for byoyomi (counting the seconds out) for each minute - usually the last 10 seconds. In our terms, you might think that that means the time allowance could be considered to be 3h 55m with 5 min overtime. But even that is wrong. A player does not lose if he uses up his first minute of byoyomi. He just goes down to 4 byoyomi sessions and so on. If he plays his move within 1 minute, no time is taken off at all. In the old days, often no time was taken off even if the player exceeded one minute. The young timekeepers learned to count v...e...r...y slowly. Might still be the case - no sponsor wants a great game to end with a loss on time. A player only loses on time if he finally exceeds the X hours of counted time. In reports, where a player makes full use of his time allowance, this is given as "time used: 4h 59m." The actual time spent could have been up to a couple of hours longer than that.

5 hours is definitely quite far from the forays of Mickey Mouse, haha

But on the website it just says five minutes. So is it always assumed that these are 1 minute byo-yomi periods unless stated otherwise?

Imagine Shin Jinseo getting time limits like these!