It is possible for symptoms to last less than 24 hours. It is not uncommon and simply a part of living with MS.

When referring to symptoms lasting longer than 24 hours this is in reference to an exacerbation (relapse, attack, flare-up).

An exacerbation is old symptoms and/or new symptoms lasting continuously for more than 24 hours. For it to be considered a new exacerbation it needs to be 30 days from when the previous exacerbation ended. These are guidelines.