I am not a native speaker, so please don't trust me 100% but I'd go with something like: たった１００秒の日本 or 100秒の日本 or perhaps with で if you add a verb: 100秒で分かる日本 100秒で見る日本 100秒で探検する日本 Hopefully a native speaker can clarify!

My take on it would be "100秒で日本を知ろう" This is obviously not a direct translation but the most natural I believe. I think Asher's 100秒で分かる日本　is also a really concise and simple way to say it.