I don't see an accurate way of doing it without factoring in the different months and leap years.
Shouldn't be too diffifcult.
Let's say TotalSeconds is the variable you're using:
(first the amount of years): TotalSeconds=TotalSeconds + (years*31536000)
(now the months):If month is later than January : TotalSeconds=TotalSeconds + (31*86400)
If month is later than February and NOT leap year : TotalSeconds=TotalSeconds + (28*86400)
If month is later than February and a leap year : TotalSeconds=TotalSeconds + (29*86400)
and then you're just left with the days and hours.
Of course, because you're using constant numbers for the months you wouldn't need to use maths like 31*86400 as you could use 2678400, which would mean you wouldn't need to use the brackets then either.
14 or so lines of code and you'd have your seconds stored in your variable.