Honestly, there is no universal timer that says a concrete street bench will crack after a certain number of freezing nights. In most real-world cases, a well-made concrete bench does not crack during the first frost. What usually happens is slower and less dramatic: water soaks into tiny pores and micro-cracks, freezes, expands, and creates internal stress. Repeat that cycle dozens or hundreds of times, and small flaws gradually grow into visible cracks.
If the bench is ordinary non-air-entrained concrete and it sits outside in a climate with wet winters, you may see hairline cracks or surface scaling within two to five winters. If the concrete is dense, air-entrained, properly cured, and sealed, it can easily last ten to twenty years before freeze-thaw damage becomes obvious. If there is already a crack or a chipped edge holding water, things speed up a lot. One bad winter with repeated freeze-thaw cycles can turn a hairline crack into a noticeable structural crack.
The biggest factor is water. Concrete is porous. When absorbed water freezes, it expands by about nine percent. That expansion does not sound like much, but trapped inside a pore it can generate enough pressure to break the cement paste. A single freeze may not do it, but freeze-thaw fatigue is much like bending a paperclip: each cycle weakens the material a little more. Melting snow, rain before a cold snap, or poor drainage that lets water pool under the bench accelerates the problem.
De-icing salt makes things worse. If a street bench is near a salted sidewalk or road, salty slush splashes onto the concrete, lowers the freezing point, and creates more freeze-thaw cycling while also attacking the cement paste chemically. In that case, surface spalling and cracking can appear after only one or two winters.
Rapid temperature drops can also encourage cracking. If the surface cools and contracts faster than the interior, thermal shock adds another stress. Still, for a typical concrete street bench, thermal shock alone rarely causes a sudden crack. The culprit is almost always water plus repeated frost.
So the realistic answer is: not instantly, but faster than most people expect if the bench absorbs water. You might get a few winters with no visible damage, then one spring you notice a fine crack running across the seat. From there it widens. Regular sealing, good drainage, and using air-entrained concrete are the main ways to slow the process. If you want to keep a concrete bench from cracking in freezing temperatures, keep water out, and repair small cracks before winter.