Thanks! I think it was this particular product that just wasn't clear - their website says:
Massage 2-3 drops as needed into the face, neck and décolletage, morning and/or evening.
And that's repeated on Space NK etc. so the order wasn't clear (and suggests it's not just a nighttime thing). But then the Sephora website said this:
Apply three to four drops into face and neck, morning and/or evening. Massage until absorbed, and then follow with your favorite Sunday Riley treatment or moisturizer.
Hence my attempt to use moisturiser afterwards.
Oh well, it's finished now, so all a bit academic - I'll just have to remember when I get to the Espa one in my stash! Every day's a school day...