Never give up! The following may not be what you don't understand, but I'd like to continue to explain it.
Do you know the difference between じかんたい and じかん?
じかんたい means あるじかんからあるじかんまで. じかん is a point, but じかんたい is a range.
example of the difference:
Trains that come at this time of day are always crowded.
Xe lửa đến vào thời gian này trong ngày luôn đông đúc.
The trains that come at this time are always crowded.
Những chuyến tàu đến lúc này luôn đông đúc.
じかんたい is a range. This range is flexible and depends on the object.
The time of getting sleepy in the afternoon is from two to four o'clock.
One hour before lunch is the most hungry time of the day.
Trains at the time of day when I take are crowded. The train that comes only 10 minutes later is not so crowded.
This じかんたい may be about 20 minutes. In Tokyo, trains come one after another in a very short time.