The departures are at 8 am. and 10 a.m. daily, but I suggest that your group be there at the time of the first departure because it is considerably less crowded.

considerably 是形容词 considerable 的副词形式，由 consider（考虑）加后缀 -able（能够...的）构成形容词，再加 -ly 变成副词。considerable 原意是"值得考虑的"，引申为"相当大/多的"。 considerably 作为副词，意思是"相当大地、显著地"，用来修饰形容词比较级 less crowded，表示"明显不那么拥挤"。