SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '42983e6aa70a259005699c289f30c4b67e1d8b2b643553a68f57f08d3b74f48d' 
  AND token = 'iiJLNE1JusGXH2OAWIEzTHKBcI5qAPrSu9DwjaM0Vy4=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00027

JSON explain

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