Allow three clear days for the letter to arrive.

信要整整三天才能寄到。

《牛津词典》

Though he was fast losing control of his body, his mind and voice were clear for about three days after I got home, and we had some good talks.

尽管他的身体正在迅速地不听使唤了，他的头脑和表达能力在我回来的三天里还是很清楚的，我们好好地聊了几次。

youdao

Nine days after the tsunami, there is still no clear number for the number of the people who have died on this remote cluster of more than 550 islands, of which only three dozen are inhabited.

海啸已经过去整整9天，但岛上丧生的确切人数仍然不清楚。 安达曼和尼科巴群岛由550个岛屿组成，其中只有不到40个的岛上有人居住。

youdao

The task is so difficult that the FDA has allotted three days for the work, a clear sign of controversy.

FORBES: Judgment Day For The FDA, Pfizer

Leading up to the jump, I'd had to wait for three frustrating days for the cloud cover coming from the Tasman Sea to clear clouds not only spoil the view, but prevent jumpers from spotting their landing zones.

WSJ: Sky-Diving in New Zealand