I understand what they’re trying to say here, but “opening time” actually means the time at which the gate is opened (in this case, 4:50), not the entire length of time during which it is open. A “time” generally refers to a specific time on the clock; to denote a length of time, we use the word “hours“:
X The Time Required from This Station (About-Minutes)
What is an “about-minute”? How can it take 30 about-minutes to get to Shinjuku??
Of course, actually it takes “about 30 minutes”. Literally, the translation of 「単位：約分」 should be “Unit: Approximate minutes”. But that also sounds a bit strange in English. An “approximate minute” isn’t really a unit, just like an “about-minute” isn’t.
More natural English would be to put “approximate” at the beginning. Take it out of the parenthesis. Also, I think it’s obvious that the times are from this station; instead, let’s say that the times are to each station shown on the chart.
O Approximate time required to each station (in minutes)