The noun time is countable in expressions like a long time, a short time and quite a time.

They took a long time to finish the job.
We have been hearing about this for quite a time.

Time is generally uncountable when we talk about the ‘time’ (number of hours, days etc.) needed to complete something.

He took quite some time to give a reply.

The expression ‘the time’ means ‘enough time’. Note that the is often dropped in an informal style.

Just come with me – I don’t have (the) time to explain.
Clock times

When we talk about clock times, time is countable. The countable time can be used with the indefinite articles a/an. It can also have plural forms.

Two o’ clock would be a great time to start. (NOT Two o’clock would be great time to start.)

She called me at various times yesterday. (NOT She called me at various time yesterday.)

Without prepositions

In some common expressions time is often used without a preposition.

Can you come another time? (More natural than ‘Can you come at another time?’)
What time does the bus leave? (More natural than ‘At what time does the bus leave?’)
You can’t beat me this time.

On time and in time

On time means at the planned time. When you are on time you are neither late nor early.

None of the trains arrived on time.
We want the meeting to start exactly on time.

The opposite of on time is early or late.

In time means ‘before the last moment’. It’s opposite is ‘too late’.

He would have died if he hadn’t been taken to hospital in time. (He was taken to hospital before it was too late. So he survived.)