English idiom related to time

I wonder what is the English idiom with the following meaning.

"There are two opinions and only time could decide what is true".

It should be something like "survive time's exam" or something like that.

Solution 1:

I'm not sure I agree about 'Stand the test of time'. It is used in a different sense to the one the OP is seeking. If you are, for example, unsure whether a particular product will sell in the long run, or just be a passing fad, one would ask 'Will it stand the test of time?'.

But the OP is looking for a term which indicates that time will supply the answer as to which of two opinions is correct. For example - will a vaccine for Covid-19 prove possible? In that case 'time will tell', would seem more appropriate.

Solution 2:

To stand the test of time is a reasonably fixed idiom that conveys exactly what you're trying to describe:

To remain useful or valued over a long period of time; to last a long time.

Solution 3:

I think that In the fullness of time may also be used in the context:

After a due amount of time have elapsed.

In the fulness of time we will know which is true.

Solution 4:

A fairly commonly used idiom where I live is only time will tell. It is used to convey the exact meaning you state above.