Could you explain how you caculated it?
I have set it on 1% and after testing I saw it was switching to dev pool every 50~60 min for 30~40 seconds:
[2018-06-03 03:34:24] accepted: 3036/3036 (100.00%, ping 117 ms), 35.80 MH/s Cool!
[2018-06-03 03:34:41] GPU #0: 1797 MHz 28.48 kH/W 113W 55C FAN 46%
[2018-06-03 03:34:42] accepted: 3037/3037 (100.00%, ping 97 ms), 35.80 MH/s Cool!
[2018-06-03 03:34:52] lyra2z.eu.nicehash.com:3365 lyra2z block 63009
[2018-06-03 03:34:54] Stratum difficulty set to 2
[2018-06-03 03:34:55] accepted: 3038/3038 (100.00%, ping 108 ms), 35.80 MH/s Cool!
[2018-06-03 03:34:56] accepted: 3039/3039 (100.00%, ping 117 ms), 35.80 MH/s Cool!
[2018-06-03 03:34:57] accepted: 3040/3040 (100.00%, ping 89 ms), 35.80 MH/s Cool!
[2018-06-03 03:34:57] accepted: 3041/3041 (100.00%, ping 120 ms), 35.80 MH/s Cool!
[2018-06-03 03:34:58] accepted: 3042/3042 (100.00%, ping 97 ms), 35.80 MH/s Cool!
[2018-06-03 03:34:59] accepted: 3043/3043 (100.00%, ping 107 ms), 35.80 MH/s Cool!
[2018-06-03 03:34:59] accepted: 3044/3044 (100.00%, ping 100 ms), 35.80 MH/s Cool!
[2018-06-03 03:35:00] accepted: 3045/3045 (100.00%, ping 106 ms), 35.80 MH/s Cool!
[2018-06-03 03:35:00] dev pool lyra2z block 105089
[2018-06-03 03:35:05] accepted: 3046/3046 (100.00%, ping 105 ms), 35.80 MH/s Cool!
[2018-06-03 03:35:06] accepted: 3047/3047 (100.00%, ping 127 ms), 35.80 MH/s Cool!
[2018-06-03 03:35:07] accepted: 3048/3048 (100.00%, ping 113 ms), 35.80 MH/s Cool!
[2018-06-03 03:35:08] accepted: 3049/3049 (100.00%, ping 108 ms), 35.80 MH/s Cool!
[2018-06-03 03:35:08] accepted: 3050/3050 (100.00%, ping 102 ms), 35.80 MH/s Cool!
[2018-06-03 03:35:09] accepted: 3051/3051 (100.00%, ping 106 ms), 35.80 MH/s Cool!
[2018-06-03 03:35:09] accepted: 3052/3052 (100.00%, ping 100 ms), 35.80 MH/s Cool!
[2018-06-03 03:35:09] accepted: 3053/3053 (100.00%, ping 103 ms), 35.80 MH/s Cool!
[2018-06-03 03:35:10] accepted: 3054/3054 (100.00%, ping 105 ms), 35.80 MH/s Cool!
[2018-06-03 03:35:11] accepted: 3055/3055 (100.00%, ping 110 ms), 35.80 MH/s Cool!
[2018-06-03 03:35:12] accepted: 3056/3056 (100.00%, ping 97 ms), 35.80 MH/s Cool!
[2018-06-03 03:35:12] accepted: 3057/3057 (100.00%, ping 96 ms), 35.80 MH/s Cool!
[2018-06-03 03:35:13] accepted: 3058/3058 (100.00%, ping 117 ms), 35.80 MH/s Cool!
[2018-06-03 03:35:14] accepted: 3059/3059 (100.00%, ping 104 ms), 35.80 MH/s Cool!
[2018-06-03 03:35:16] accepted: 3060/3060 (100.00%, ping 111 ms), 35.80 MH/s Cool!
[2018-06-03 03:35:16] accepted: 3061/3061 (100.00%, ping 103 ms), 35.80 MH/s Cool!
[2018-06-03 03:35:16] accepted: 3062/3062 (100.00%, ping 101 ms), 35.80 MH/s Cool!
[2018-06-03 03:35:17] accepted: 3063/3063 (100.00%, ping 103 ms), 35.80 MH/s Cool!
[2018-06-03 03:35:18] accepted: 3064/3064 (100.00%, ping 125 ms), 35.80 MH/s Cool!
[2018-06-03 03:35:20] accepted: 3065/3065 (100.00%, ping 111 ms), 35.80 MH/s Cool!
[2018-06-03 03:35:22] accepted: 3066/3066 (100.00%, ping 102 ms), 35.80 MH/s Cool!
[2018-06-03 03:35:24] lyra2z.eu.nicehash.com:3365 lyra2z block 63009
[2018-06-03 03:35:26] accepted: 3067/3067 (100.00%, ping 127 ms), 35.80 MH/s Cool!
[2018-06-03 03:35:28] accepted: 3068/3068 (100.00%, ping 110 ms), 35.80 MH/s Cool!
[2018-06-03 03:35:28] accepted: 3069/3069 (100.00%, ping 20 ms), 35.80 MH/s Cool!
[2018-06-03 03:35:28] accepted: 3070/3070 (100.00%, ping 91 ms), 35.80 MH/s Cool!
[2018-06-03 03:35:29] accepted: 3071/3071 (100.00%, ping 115 ms), 35.80 MH/s Cool!