"finish" 是一个动词，它的完成时态是 现在完成时。现在完成时的构成是使用动词的过去分词加上助动词 "have" 或 "has"。例如：

1. I have already finished my homework.

2. They will be weeks before they finish doing their homework.

需要注意的是，"finish" 是一个非延续性动词，通常不与 "for"、"since" 等时间状语连用。如果需要表达完成的状态，可以使用 "over" 替换 "for"，例如：

The film has been over for 3 hours.

此外，"finish" 还可以与其他时态结合使用，例如过去完成时：

She had finished her homework before her brother arrived.