The Rule of 3s is a general guidelines for the adjustment period of a pet to their new home. Every dog and cat is unique and will adjust at their own pace. Give them the time and space to do so.
to decompress and relax
Your new foster pet may feel overwhelmed with their new surroundings. Don't be alarmed if they don't want to eat for the first few days. They may be scared and unsure what is going on, or may be the oposite and test you to see what they can get away with.
to learn the routine
Your foster pet is starting to settle in feeling more comfortable and realizing this is their home for now; figuring out the environment and getting into the routine that you have set. You may start to see their real personality. Behavior issues may start showing, so this is your time to start helping them learn what is right and wrong.
to start feeling at home
Your foster pet is now completely comfortable in your home. You have built trust and a bond with them, which gives your foster dog or cat a complete sense of security with you. They have set into a routine and will come to expect dinner at the usual time.