Matching time values problem

I have a calculation which gives an average of several "time" fields - HH:MM:SS so far so good.

I also have a target scale which effectively says that if the aforementioned average falls within a certain range, it scores a 10. (there are actually 9 ranges in total)

Most of the time all this works ok, until the average equals one of the starting figures for a range.

Essentially it's a very simple calc that divides a total call time duration by the number of overall calls, in one case this ends up as 00:03:20, which is identical to the start of one of the ranges (00:03:20 - 00:04:00), but as mentioned, it doesnt see it as a match.

Now I figured out that this is because in actuality the avg and the time, whilst displayed the same actually arent, so I used the floor function =iferror(floor(sum(cell1 / cell2),1/24/60/60),1)) to bring my avg in line. This solved most of the problem, or so I thought. There is one number that when I translate both back to a number, the eighth or ninth digit is one out (I think on the number it's an 8, on my average it's a 7).

So my question is, is there any way of getting Excel to always match up two time values - one from an average - one from a straight time value?

*I dont really want to have to mess about with the range times I have put in (so keep it as a simple HH:MM:SS), as a lot of other stuff relies on this, so would ideally be looking to get my average to match the range.

I'll give it a go when i get to work, but I tried =mround(a1, 1/864000) yesterday and it didnt seem to work.

Sadly I have to have it to the nearest second. Who would have thought it would be so hard!

Anyone have any ideas at all?