How often do I need to remove poo and stir the silica litter?
You'll need to remove poo regularly and stir the litter at least once every day. This allows the water component in the urine to evaporate while the urine waste is absorbed into the litter itself.
If you are going to be away from the litter box for a couple days, it should be okay, but this should be considered an exception. For example, if you head out of town for a weekend you can leave your litter box unattended, but you won't want to leave it unattended during a week in the Bahamas. ;)