1) Asap 2) At the earliest date 3) At the earliest opportunity 4) At the first opportunity 5) Earliest 6) Earliest date 7) Earliest time 8) Happening first 9) In the least time 10) Least delayed 11) Most promptly 12) Most quickly 13) Next 14) Next available 15) Quick as can be 16) Superlatively early 1) Earliest 
[adv] - with the least delay
earliest adverb with the least delay; `the soonest I can arrive is 3 P.M.`