SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '8666d5cf8e377ed15749d2d3b753f34f80a3663f8d15e16a33447303dd78c486' 
  AND token = '/866pET3jKaiMDhuiaX4yV+stoeGV6mH1GEUg/08QgE=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00022

JSON explain

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