50 and 55 minutes as base time control

i would like to play some game at 50+15 time control, i think it would be good for me, but it is not possibile to select 50 or 55 minutes as base time control. I think it makes sense to add this options. I know 40 + 20 and 60 + 10 are similar but i think 50 + 15 or 55 +12 can be better, because the increment should not be too long and it should not be too short