Speed graph has 6 columns: can the 5min period be changed to 6min

[markygnlg]

All the speed graphs 'periods' are divisible by 6, other than 5mins, ie:
1mins / 6 = 10secs
30mins / 6 = 5mins
6hrs / 6 = 1hr
12hrs / 6 = 2hrs
24hrs / 6 = 4hrs

However the 5 minute period is 0.833mins per column (50 seconds).
I know it's a small difference but I have a reason to ask for this change (it's not an important but worth asking for a change).

Thanks for such a great & reliable program!