Meaning:

Something will be clear sometime in the future, not now, whether it is good, bad, successful, a mistake, etc.

If you say "Time will tell," you mean that you will not know whether something is good or bad until sometime in the future.

People also say "Only time will tell."

Example:

Only time will tell whether we elected the right person.

Don't worry now; we've done everything we could do. I don't see any problems in our decision, but time will tell.

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