请教关于time 的可数不可数问题

time为什么有时候可数有时候不可数

作时间时，不可数名词。作次数或倍数时是可数名词。

表“时间”为不可数名词,但是有些是习惯形成的可数如,have a good time ;a long time
表示“次数、倍数”是可数名词
不能算

这里的 time 表“时间”，是用作不可数名词，但又可与不定冠词“a”连用。经查证，多数权威词典均将其列为不可数名词：
1.《21世纪英汉汉英双向词典》
(U) [又作 a time] (某一) 期间,某一段时间。
for a time 暂时；一时；
after a time 过一会儿；
in a short time 不久;
It's a long time since I met you last. 好久不见 [久违] 了。

2.《柯林斯高级英语学习词典》
[N-UNCOUNT] also a N。
For a long time I didn't tell anyone. 很久我都没有告诉任何人。
A short time later they sat down to eat. 过了一小会儿，他们坐下来吃东西。

3.《牛津高阶英汉双解词典》
[U] portion or measure of time 一段时间：
What a (long) time you've been! 你花费那麽长的时间了!
I had a most unpleasant time at the dentist's. 我在牙医那里受了大罪。

4.《剑桥高级学习词典》
noun [U]
I enjoyed my course at first, but after a time I got bored with it.
They stayed with us for a short time.

5.《朗文当代英语词典》
【PERIOD OF TIME】 [singular, U]
I first met Jennifer a long time ago.
They stopped for a short time to rest the horses.

但《麦克米兰英语词典》
[count] a period:
She thought about it for a long time.
The company only started trading a short time ago.