SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '7462afc15b14a68dbf91cb1d9ddf0328f6734cde8e7e564485758f4f577d7860' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00019

JSON explain

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