SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '8449c72bc38cc9d13c23cb56240330a901d7d7f67434556d05258ba0e8b66347' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00023

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "message": "Impossible WHERE noticed after reading const tables"
    }
  }
}