Once they know it's there and are use to it, not long. Between January and August probably no more than 2 weeks depending on deer density, how many others are feeding protein and other things. Put it near a water source.
It will depend on how many deer you are seeing at that location. If you are seeing 20 deer then it will last 6-7 days once they get on the feed good. Less deer it will last longer and more deer will empty it much faster. At first it will last longer than when they have been on feed a while and it gets really dry. 2 yrs ago I had one 275# cap feeder going empty every 6-7 days in the summer months. Last year it lasted a month. Same feeder and same amount of deer just it rained 45" and I had good food plots.