SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '51a3c9c224fd7734d15d672c48ff9ca3df3ebe5fd0031c99d3a1e588f4e0a203' 
  AND token = 'NlUTXITmLjzAUsXJqIqwqigeLOL6oDdRlWxokHsUL54=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00035

JSON explain

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