SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '20711e73632e90dfe5d16f4cfbe34c1dea6630c93228ff66a01323797380d30f' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00033

JSON explain

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