Which English form is correct:
Time flies so fast or Time fly so fast ?

2

It is important to make sure the subject (time) agrees with the verb (to fly). In this example, time is singular, so the verb must use the singular form flies.

Time flies so fast

It's correct

This is a common idiom used in English to indicate that time seems to pass more quickly in certain situations.

More...

Preferred Form

Time flies so quickly

Time fly so fast

It's not correct. Don't use this phrase.

Subject-verb agreement:In this phrase, the subject, time,is singular (like he, she, or it), so it requires the singular verb, flies.

Preferred Form

Time flies so quickly