With the door kept shut, a refrigerator keeps food safe for up to about 4 hours; a full freezer lasts about 48 hours and a half-full one 24 (USDA and foodsafety.gov, for household appliances). No single number fits everyone, because three things set the time.
A full cabinet warms far more slowly than an empty one because the product mass carries the cold. Every door opening takes time off, and an outage in midsummer lasts far less than one in winter. A temperature probe is enough to watch without opening the door, and frozen plates or water-filled containers put in before the outage give cold without electricity.
After the outage the decision depends on the highest temperature the product reached and how long it stayed there. For chilled food such as meat, poultry and fish, more than 2 hours at 4 °C or above is a reason to discard. Frozen food that still has ice crystals, or is at 4 °C or below, can be refrozen, though quality may suffer.
Measure your own cabinet's figure on an empty weekend: switch it off empty, watch the temperature without opening the door and write down how many hours it takes to reach the threshold.