It depends on where we draw the starting line. We're already at parity with 3.5BYA to 541Mya because no neurons existed in that duration. Only more recently, in the Cambrian, do we have evidence that voltage gated potassium signaling evolved[1].

That changes the calculus likely very little, but it feels more accurate.

1. https://www.cell.com/current-biology/pdf/S0960-9822(16)30489...