I think the highlighted move above 7...h5 makes the mate faster, because the trick is to delay everything and 7...h6 could be stronger and might hold the mate longer.
After 7.Nc2 I get a line with Ka6 as main line. But it is still M18. Stockfish MOD was not doing very well
But my hardware also is probably not up to it compared with what Vincent sometimes uses. Then I stopped Stockfish MOD and fired up old Rainbow Serpent and it has much less problems
qrb5/bkPp3p/1p1B4/1p1KP3/1P2Pp2/R4P1p/P3pP1P/4N1n1 w - -
Engine: Rainbow Serpent 20170105 HT (512 MB)
by T. Romstad, M. Costalba, J. Kiiski, G.
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34/55 1:10 +5.11++ 1.Kd4 (886.311.709) 12610
34/55 1:11 +5.19++ 1.Kd4 (899.100.972) 12630
34/55 1:11 +5.31++ 1.Kd4 (900.683.988) 12631
34/55 1:11 +5.48++ 1.Kd4 (903.394.182) 12632
34/55 1:16 +5.71++ 1.Kd4 (970.436.865) 12646
34/55 1:17 +6.02++ 1.Kd4 (975.725.512) 12640
34/55 1:17 +6.42++ 1.Kd4 (979.207.674) 12639
34/55 1:18 +6.95++ 1.Kd4 (986.463.745) 12638
34/55 1:18 +7.62++ 1.Kd4 (991.287.814) 12634
34/55 1:19 +8.48++ 1.Kd4 (998.534.909) 12628
34/55 1:19 +9.57++ 1.Kd4 (1.001.198.678) 12628
34/55 1:19 +10.95++ 1.Kd4 (1.003.372.180) 12625
34/55 1:19 +12.84++ 1.Kd4 (1.007.916.346) 12621
34/55 1:19 +15.18++ 1.Kd4 (1.008.335.590) 12621
34/55 1:19 +17.97++ 1.Kd4 (1.008.986.187) 12621
34/55 1:19 +21.48++ 1.Kd4 (1.009.433.215) 12621
34/55 1:20 +27.06++ 1.Kd4 (1.010.166.187) 12622
34/55 1:20 +32.53++ 1.Kd4 (1.010.849.623) 12622
34/55 1:20 +39.39++ 1.Kd4 (1.011.304.206) 12622
34/55 1:20 +47.99++ 1.Kd4 (1.011.654.446) 12623
34/55 1:20 +58.76++ 1.Kd4 (1.012.057.839) 12623
34/55 1:20 +72.23++ 1.Kd4 (1.012.358.610) 12623
34/55 1:20 +89.10++ 1.Kd4 (1.013.026.574) 12623
34/55 1:20 +110.19++1.Kd4 (1.013.410.172) 12623
34/64 1:26 +M25 1.Kd4 h5 2.Kd5 h4 3.Kd4 Kc6 4.Rc3+ Kb7
5.Kd3 Ka6 6.Ra3+ Kb7 7.Kd2 Kc6
8.Rc3+ Kb7 9.Nc2 Ka6 10.Ra3+ Kb7
11.Nd4 e1R 12.Kxe1 Ne2 13.Nxe2 Kc6
14.Rc3+ (1.084.146.228) 12500
35/64 1:45 +M21 1.Kd4 h6 2.Kd3 Kc6 3.Rc3+ Kb7 4.Kd2 Ka6
5.Ra3+ Kb7 6.Nc2 Kc6 7.Nd4+ Kb7
8.Ke1 h5 9.Kd2 e1R 10.Kxe1 h4 11.Kd2 Ne2
12.Nxe2 Kc6 13.Rc3+ Kb7 14.Nxf4 (1.292.416.841) 12229
36/64 1:55 +M21 1.Kd4 Kc6 2.Rc3+ Kb7 3.Kd3 Ka6
4.Ra3+ Kb7 5.Kd2 Kc6 6.Rc3+ Kb7
7.Nc2 Ka6 8.Ra3+ Kb7 9.Nd4 h6 10.Ke1 h5
11.Kd2 e1R 12.Kxe1 h4 13.Kd2 Ne2
14.Nxe2 (1.394.077.378) 12114
37/64 2:10 +M20 1.Kd4 Kc6 2.Rc3+ Kb7 3.Kd3 Ka6
4.Ra3+ Kb7 5.Kd2 Kc6 6.Rc3+ Kb7
7.Nc2 Ka6 8.Ra3+ Kb7 9.Nd4 e1R
10.Kxe1 h5 11.Kd1 Ne2 12.Nxe2 Kc6
13.Nd4+ Kb7 14.Ke1 (1.563.525.277) 11944
38/64 2:30 +M19 1.Kd4 Kc6 2.Rc3+ Kb7 3.Kd3 Ka6
4.Ra3+ Kb7 5.Kd2 Kc6 6.Rc3+ Kb7
7.Nc2 Ka6 8.Ra3+ Kb7 9.Nd4 Nxf3+
10.Nxf3 Kc6 11.Nd4+ Kb7 12.Kxe2 h6
13.Ke1 f3 14.Nf5 (1.771.178.942) 11768
39/64 3:14 +M19 1.Kd4 Kc6 2.Rc3+ Kb7 3.Kd3 Ka6
4.Ra3+ Kb7 5.Kd2 Kc6 6.Rc3+ Kb7
7.Nc2 Ka6 8.Ra3+ Kb7 9.Nd4 Nxf3+
10.Nxf3 Kc6 11.Nd4+ Kb7 12.Kxe2 h6
13.Ke1 f3 14.Nf5 (2.250.390.980) 11599
40/64 4:01 +M18 1.Kd4 Kc6 2.Rc3+ Kb7 3.Kd3 Ka6
4.Ra3+ Kb7 5.Kd2 Kc6 6.Rc3+ Kb7
7.Nc2 Ka6 8.Ra3+ Kb7 9.Nd4 Nxf3+
10.Nxf3 h6 11.Nd4 h5 12.Ke1 h4
13.Nf3 Kc6 14.Rc3+ (2.769.791.473) 11490
41/64 5:55 +M18 1.Kd4 Kc6 2.Rc3+ Kb7 3.Kd3 Ka6
4.Ra3+ Kb7 5.Kd2 Kc6 6.Rc3+ Kb7
7.Nc2 Ka6 8.Ra3+ Kb7 9.Nd4 Nxf3+
10.Nxf3 h6 11.Nd4 h5 12.Ke1 h4
13.Nf3 Kc6 14.Rc3+ (4.035.747.288) 11356
42/64 7:50 +M18 1.Kd4 Kc6 2.Rc3+ Kb7 3.Kd3 Ka6
4.Ra3+ Kb7 5.Kd2 Kc6 6.Rc3+ Kb7
7.Nc2 Ka6 8.Ra3+ Kb7 9.Nd4 Nxf3+
10.Nxf3 h6 11.Nd4 h5 12.Ke1 h4
13.Nf3 Kc6 14.Rc3+ (5.322.011.547) 11310
43/64 10:18 +M18 1.Kd4 Kc6 2.Rc3+ Kb7 3.Kd3 Ka6
4.Ra3+ Kb7 5.Kd2 Kc6 6.Rc3+ Kb7
7.Nc2 Ka6 8.Ra3+ Kb7 9.Nd4 Nxf3+
10.Nxf3 h6 11.Nd4 h5 12.Ke1 h4
13.Nf3 Kc6 14.Rc3+ (6.955.268.302) 11254
Chest solutions are not always the shortest, that depends on the parameters used. More strict parameters mean longer computations.