SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'aaf6fa7bf6f8d9be7e292501d7f4dcc988f3c1bb1dfd43889253b0285bca803f' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00026

JSON explain

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