SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '251d8bf09dad1af8b8667b55ac8c4ec0209a6e6a1f26523b182751d3afb40743' 
  AND token = 'JMaLAsrBAAplIMGZr3yd920o+xNZFOFkPnQsun54Bko=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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