From the EWTN devotional section:FOREWORD
The novena in honor of the Holy Spirit is the oldest of all novenas since it was first made at the direction of Our Lord Himself when He sent His apostles back to Jerusalem to await the coming of the Holy Spirit on the first Pentecost. It is still the only novena officially prescribed by the Church. Addressed to the Third Person of the Blessed Trinity, it is a powerful plea for the light and strength and love so sorely needed by every Christian.
This Novena begins on the 6th Friday of Easter, or the Friday following Ascension Thursday. In the Diocese of the United States, Ascension has been moved to Sunday, but the Novena still begins this coming Friday.
These kind of devotions, which have been around for centuries, and in some cases since the early days of the Church have be downplayed for the last 40 years. One has to wonder how many Catholic saints engaged in prayers of this kind. If you are born after Vatican II like me, and have never had exposure to this kind of devotion, consider giving God just 15 minutes per day for the 9 days between Ascension Thursday and Pentecost. If you were born before Vatican II and stopped doing devotions like these, it's time to bring some into your day. If you already do them no more convincing is necessary.
If you don't think you have time, take a close look at how much time you give the TV, the computer, a hobby, sports, or just hanging out and compare that to how much time you give God.
Link to the Novena of the Holy Spirit