Easier division of interval?

[ryofurue]

I may well be missing something but it seems that currently you can't do this:

using Dates
t1 = DateTime(2017,7,1)
t2 = DateTime(2017,7,1,6)
tm = t1 + (t2 - t1)/7  # 1/7 of the way from t1 to t2

I need to do this a lot to interpolate times. As far as I can tell, the following is the only robust way to do it:

tm = t1 + Millisecond(round((t2 - t1) / Millisecond(1))/ 7))

I know the integer division (÷) works, but it doesn't do rounding.

Intervals behave like an integer, but for the actual integer, the following method is standard:

t1 = 0
t2 = 6
tm = t1 + round(Int, (t2 - t1)/7)

This works because Int/Int results in Float64.

This discussion suggests that we perhaps need a special division function:

divround(i::Millisecond, x::Real, roundingmode = RoundNearest) =
   Millisecond( round(i / Millisecond(1) / x, roundingmode) )
tm = t1 + divround(t2 - t1, 7)

In this way, the user can remain ignorant of the fact that Millisecond is the best unit to divide an interval (so that if/when DateTime starts to include microseconds, the user doesn't have to change her code).

Or perhaps we want to create a FloatingpointMillisecond type which would be to Millisecond what Float64 is to Int?