There isn't any definitions for al primo on both The Concise Oxford Dictionary of Music and Harvard Dictionary of Music, 2nd Edition. I made a quick research and al defined as 'in the manner of' on this web site. And primo usually means 'principal'. Such as it is in tempo primo.
I suggest that it refers to 'a tempo' rather than a repeat. Because, regarding the style of baroque period, you usually repeat the minuet 1 after minuet 2 and minuet 2 usually creates a contrast with minuet 1, like a minuet sandwich. Thus, I think the composer or most probably the editor intended to say 'repeat the first minuet but not as slow as you play the second minuet.'
Another option might be the composer or again most probably the editor intented to express that you don't have to play with variations when you play the first minuet for the second time. This is because depending on the baroque period style you usually make variations when you repeat a minuet, or even a phrase. Therefore al primo might be a stylistic expression to limit or navigate the performer.
My last suggestion is the composer created a piece out of style -which I'm accustomed to thanks to J.S.Bach- and wanted the performer to repeat the second minuet rather than turning back to first minuet but faster this time. In other words; minuet 1(fast) minuet 2(slow) again minuet 2(but this time fast.). Please note that I assumed your first minuet is fast, and the composer wrote an idiomatic piece.
It'd beneficial to listen to the records, especially the ones that played by artists who don't primarily aim to earn a lot of money (which is not a bad thing). Because 'othantic' records usually doesn't sell much, moreover, most performers don't know the baroque style but they know the rules of the revised one. Luckily, I had the chance to study with one of the masters; it's like a beautiful ocean, I just touched my foot to the sea.