It only says it is a noun and in singular number.
Quassnoi is right asking what dictionary doesn't have the gender mark for the word часы. For example, wikidictionary specifies that the gender is masculine as well as it specifies that the word is only used in plural.
Other dictionaries, which I checked, for example Щерба, Матусевич. Русско-французский словарь, 1993, only specify plural, and no gender for часы.
Not specifying gender for the words that are only used in plural makes sense for Russian language because their gender has only historical value and does not manifests itself grammatically in any way. In Russian neither endings of adjectives, nor endings of verbs will differ when they are related to plural nouns of different genders. Compare with French which differentiates gender in plural via adjective endings:
palissades vertes (fem.) - зелёные заборы
feux verts (masc.) - зелёные огни