Just looking at transition speed from those who developed a La Nina as forecast and we're at least moderate at peak.
63/64: +1.4 to -0.6 was 6 months.
73/74: +2.1 to -0.5 was 5 months.
83: +2.2 to -0.5 was 8 months.
87/88: +1.7 to -0.9 was was 9 months.
94/95: +1.1 to -0.5 was 8 months.
97/98: +2.4 to -0.8 was 7 months.
09/10: +1.6 to -0.7 was 6 months.
15/16: +2.6 to -0.5 was 8 months.
Closest decline thus far is 1998 and 2016. We are tracking about a month ahead of 98 and 2 months quicker than 16 given the same pace but lower peak.
So current tracking suggests 6 months which is at least -0.5 in MJJ.
First year Nina's declared by MJJ are 54, 64, 73, 88, 07, 10.