A good range for your room should be between 0.2s and 0,5s approximate. Depend on the type of mixing or mastering, electronic music or classic, decreasing reverb time you will have a drier room, increasing reverb time you will have more liveness.
RT60 show you the timbre and tone of your room.
For example, A room with a very short time on 4/8khz bands will sound dead, a room with a long time on 63hz will sound boomy.
“A lot of people only looks at the frequency response of the room. If you have a smooth frequency response and disparate rt60 or decay times, your mixing will be inaccurate and unbalanced“
Here a great RT60 simulator.
Bob golds calculator will show RT60 ITU/EBU Control Room Recommended.After your room is controlled acoustically is the time for the final tweaks, where you will choose the liveness in your room.