Im thinking of doing medieval astrology course or splurging on a thorough horary course.
Actually the two are not separate. It is generally held that Horary originated in the early Medieval period, although recently there have been claims that the late Hellenistic Astrologer, Hephaistion of Thebes had a Proto-Horary in his Apotelesmatics Book III. Even if we take the later date and accredit it to the period of Sahl bin Bishr and Masha'allah we are still 700 years before Lilly. Indeed Lilly draws heavily on the Medieval tradition. The techniques that Lilly uses are those of Medieval Astrology.
It is possible to learn Horary without any real knowledge of the Medieval approach, indeed that's how I came to it. It fired a fascination with the techniques and an attempt to read more on Medieval Astrology. I found it quite difficult doing that from books and your suspicion of the few hours a week is well founded.
In the end I went to the beginning (LOL) and approached Medieval Astrology from it's beginning by studying the Hellenistic Approach, doing a course run by a prominent current Astrologer who uses the Hellenistic Approach.
So if you decide to take on the Medieval approach you need someone who knows what they are talking about. But you will find it very rewarding.
On the Horary side, there are several prominent teachers. Olivia Barclay's Qualified Horary Practitioner (QHP) is the most prestigious and is now run by Barbara Dunn (who published Horary Astrology Re-examined). You might also look at Deborah Houlding and Sue Ward, both of whom teach a Lilly style approach, similar to the QHP,
You will also find some courses that look at Horary from a Mediaeval perspective. My tutor, Chris Brennan runs such a course.
Incidentally, Olivia Barclay was heavily influenced by the earlier work of David Appleby, the forgotten father of the Horary revival (mainly because Barclay did not give him the credit for some of the material she used.) His book
Horary Astrology, the Art of Astrological Divination is still in print.