after two days' wait /after a two days' wait

问题描述:

after two days' wait /after a two days' wait
after a day's wait
take a half an hour's rest还是:take half an hour's rest
take a two days' rest还是:take two days' rest
take a day's rest
怎么看的呢?请说明为什么,以及语法

after two days' wait
take half an hour's rest
take two days' rest