Is there a way to turn on the air conditioning only on certain days?
If the camp has internet access, you may want to look into a WIFI-controlled thermostat. Most allow you to remotely monitor and control the temperature through a mobile phone app or with a laptop web interface. This will allow you to have the most versatile control over your temperature settings. The only other piece of equipment you'll need to make this work is a compatible wireless router - you won't need to install an entire home automation system.

Otherwise, you need a true 7-day programmable thermostat. Check the specifications on the package, because each one will have different capabilities. The one I have allows for four different temperature settings per day, for all 7 days of the week individually. You may not need something with that high of a resolution, and can get by with a single set temperature for each day of the week. The general rule will be the less features a thermostat has, the lower the price.

There are also thermostat models labeled as 5-1-1 and 5-2, which allow separate temperature settings for Saturdays and Sundays. Note that a 5-2 will only allow a single setting for the weekends. As Chris mentions, you could fudge the week day settings and get by with one of these.