No, I'm saying that you have to make sure the next weather is the correct one.
Say you arrive early at 0730, and the current weather is correct, but the next weather is wrong. When 0800 comes around, it will appear to be the correct weather still for about five Eorzea minutes. Many people see this and think they can flag the vista. However, despite appearances, the whether actually had already changed exactly at 0800, so the conditions for the vista were not met.
If a vista opens at 0000, 0800, or 1600, you have to make sure that the weather after that time is correct, because the whether changes at those exact times.