Sources on the internet state, and I agree, that the standard is to call it Daylight Saving Time (no -s on saving)
I recommend just remembering this, but some people like rules, so here’s my attempt:
Consistent with the rule that nouns that function as adjectives are never plural (except the word sport, as in sports bar, or sports team), if you put the gerund (noun) saving in front of the word time, there is no need for an -s ending on saving.
However, the rule is challenged when you use the word saving to modify bond or account, which become savings bond and savings account.
Incidentally, in 2010 in the United States (but not all states), Daylight Saving Time begins on November 7, 2010 at 2:00 am.