SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = 'f5f944cf9aceb0eead31d4027558f2277d948df7247b36346ec6291f06a7ca2d' 
  AND token = 'mMfubUnNqHNWJviBW+vXmvdWyeK5AmRrxCZULdLNh00=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00025

JSON explain

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