The original term is spelled as shown in the title, using the singular saving. The plural version, daylight savings time, is a more recent variant that remains less preferred in writing though may still be considered acceptable in general use. And if you wish to avoid introducing the unlikely miscue of whether saving refers to daylight or time, you may hyphenate the first two words. Thus, daylight saving time, daylight-saving time, and daylight savings time are all acceptable and standard, though the first two versions are preferred.
When referring to a specific time zone or specific time, saving will often be omitted (e.g., Mountain Daylight Time or 2 a.m. daylight time).