The Star Wars universe use the Standard Day as reference, which is based on the planet Coruscant, which had nearly the same rotation period as Earth.
That means the galactic calendar have 365 days1, each day have 24 hours, called standard-hour. There is no leap year in the galactic calendar.
Of course different planets can have a duration of the "day" - as time with sunlight - totally different (multiple stars, different rotation period...).
Usually character refer to "rotation" instead of day. Usually "rotation" refer to the Standard Day (which means 24h, the rotation time of Coruscant), but it can refer to local rotation (the day/night cycle of the current planet).
The canon reference book Smuggler Guide states that you can express a specific point in time within a day in hours and minutes, and its written without separators, 17:10 for example became 1710.
In Episode IV: A New Hope Han states that the estimate time to arrive to Alderaan is 0200 hours from their position.
The standard year is often referred as 368 days long as stated in The Essential Atlas but The Essentials Guide books are not canon, meanwhile in the canon Star Wars: Absolutely Everything You Need to Know is stated that the standard year is only 365 days long.