Collagen supplements are taken in one of two different forms, either in the form of hydrolyzed collagen or in the form of an undenatured type II collagen; both forms have different dosing strategies and while their benefits may share some similarities can be considered two different supplements.
Hydrolyzed collagen is taken in doses of around 10g a day for skin health and some benefits to joints, and can be taken with meals. It should not be taken in higher doses as a protein supplement (for muscle gain and fat loss) due to having less efficacy than other protein sources and a lackluster amino acid profile.
Undenatured collagen is taken at a lower dose of approximately 40mg once daily for the treatment of osteoarthritis and rheumatoid arthritis when there is an autoimmune component to it, and while it doesn't need to be taken at any particular time of the day it may be ideal to take it on an empty stomach before breakfast.