Elastics have their strongest effect during the day, when we are active and talking. This stretches the elastics dynamically, which increases the force applied to the teeth and helps to correct the bite. At night, while we sleep, the elastics mainly hold the position that has already been achieved, but they don't apply the same level of active pressure.
If the elastics are being used to correct a specific problem with the position of the teeth, rather than simply as a supporting element, they must be worn all the time. Even short breaks of a few hours can lead to a significant loss of effect and slow down your progress. Wearing them constantly makes them as effective as possible and gets you to the results you want sooner.
This answer is for general information. Your own case needs an examination by an orthodontist.