Arduino Uno +SIM900+Attiny85+DHT22

Hi guys, so far i have made a project measuring temperature and humidity data with DHT22 sensor and send the data with SIM900 as a message to a cell phone. I use Attiny85 connected to a mosfet to wake arduino every 6 hours to take measures and send the data. But now i want to wake arduino once a day at a specific time . Is this possible to do it with Attiny or i should install RTC? And if i have to install RTC how should i connect it with the already project?

I wonder about the purpose of the ATtiny and of the MOSFET. If these are required to turn power on/off, try to connect the RTC to the ATtiny.

Because the project is powered with batteries i used attiny and mofet for low power consumption. My question is : if i use rtc for alarming the arduino once a day where should i write the alarm code for the rtc? Should be written with the main programme for the arduino or should i write a seperate code and upload it firsty on the rtc?

As you like. If the RTC alarm time has to be changed more often, the Uno can hold such code.