I found it the most fundamental block in my progress - but my tutor never even mentioned it - which seems odd, looking back.Mine was really early. I don't know how long I'd been playing a kit (I started on snare)--it might have been six months, it might have been over a year--but I was trying and trying and trying to get a kind of Motown pattern going: snare on 2 and 4, kick on 1 and &3, but with quarter notes on the hats. I could play the pattern no problem as long as I played eighth notes on the hats, but whenever I switched to quarter notes, my right hand would follow my right foot and play along with the kick, rather than staying consistent. It was so frustrating and I felt so stupid but I just kept trying and trying and I can still feel the rush of that very first time I separated the two limbs and achieved the most rudimentary limb independence. It was so freeing and I felt like I'd unlocked some magical mystery.
Of course, it's all been downhill from there.
Rob Brown fixed it for me. (You need to fixate on the stick up stroke - then the two beats are separated far enough for the brain to identify and latch on to the feel)