数到3（4，5等）
when a particular number is reached
On the count of three, I'd like you all to stand up. 我数到3时希望你们全都起立。
On the count of three, they threw their grenades into the trench and ran.
We'll both start at the same time. On the count of three - one, two, three, go!
The stage manager told the actors to stay backstage and, on the count of five, he'd wave them back on.
Stay calm - we'll help you up on the count of three. Ready?
See also: count noun (NUMBER)