They won’t live long in the jar, so it doesn’t really work as an ‘in case of emergency’ type thing. I like to keep 2 batches of bbs going. Feed the 48 hr old batch. Longest you would have to go if something weird happened is 8-12 hrs before the next batch is ready.
another way would be to create a rotating set of jars. Make a big batch initially, then separate into 2 jars. Feed 1 right away, store the other in the fridge until the next batch is ready. Feed the batch from the fridge, then put the new batch in the fridge. Repeat