SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = '242f5ff757fe1b9c81f5c59f9deec720d0b09e64d793b99c8416d48a5d851850' 
  AND token = '16lVQ56N+ZjSokX/MxUnNCzuOfDDvaUogBhQ/LlYJBA=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00033

JSON explain

{
  "query_block": {
    "select_id": 1,
    "message": "no matching row in const table"
  }
}