No, it keeps quite long.
The multitude of bacteria, fungi and yeasts that make up kefir exude antibiotics that keep other bacteria OUT. I have had it in the fridge for a month and it was delicious.
In fact I keep adding more to the same old batch as I drink from it and have kept this jug going for overr a year so PART of the kefir is at least that old.
This keeping quality (even without refrigeration) is what made it so popular with nomadic people long before refrigeration was invented.
Ice creak and kefir eh!
I try to avoid any milk products for a couple hours before and after I drink my kefir becasue the fermentation of the fresh milk can resume in the warm stomach with noisy consequences.