Can this be used effectively to send frozen food, in a cooler bag in a box via UPS if it’ll get there in 24 hours or less.

I would stop by your local Matheson or Airgas company and get some dry ice.

Thanks for your interest in our products! The Blue Ice Weekender Pack is considered an alternative to ice; it is not guaranteed to stay cold or frozen for any amount of time as there are several variables that will effect its performance (such as the temperature of the contents when placed in the cooler, the temperature of the cooler, and the outside temperature if used outdoors).