关于你的问题，我在 Collins COBUILD English Grammar 上查到了以下解释，供你参考（重点注意其中的3-6条说明）：

1. To indicate how many times something happens, you can use a specific number, ‘several’, or ‘many’ followed by ‘times’.

We had to ask three times.

It’s an experience I’ve repeated many times since.

He carefully aimed his rifle and fired several times.

2. If the number you are using is ‘one’ you use ‘once’ (not ‘one time’) in this structure. If it is ‘two’ you can use ‘twice’.

I’ve been out with him once, that’s all.

The car broke down twice.

3. If something happens regularly, you can say how many times it happens within a period of time by adding ‘a’ and a word referring to a period of time.

The group met once a week.

You only have a meal three times a day.

The committee meets twice a year.

4. You can also use a frequency expression such as ‘once’ with a unit of time preceded by ‘every’ to say that something happens a specified number of times and on a regular basis within that unit of time.

The average Briton moves house once every seven and a half years.

We meet twice every Sunday.

Three times every day, he would come to the kiosk to see we were all right.

5. If an event happens regularly during a specific period of the day, you can use the period of day instead of ‘times’:

I used to go in three mornings a week.

He was going out four and sometimes five nights a week.

6. A regular rate or quantity can also be expressed by adding ‘a’ and a general time word. ‘Per’ can be used instead of ‘a’, especially in technical contexts.

They again ordered him to pay ten shillings a month.

I was only getting three hours of sleep a night.

...rising upwards at the rate of 300 feet per second.

He hurtles through the air at 600 miles per hour.