(Image bonus: Why 7590, then 759? K = Decimal ASCII 75, Z = Decimal 90 --had to make this one for you here 
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-publicdomain
Solution, do a "length(string) mod 2" check to choose a correct string to integer direction/translation
(if result is 0 you have something dividable by two, for example a string with length of 4 '7590', so you can add 2 chars from that string,
but i do not know how your program handle invalid integers like 75h 90m
(hours should just go to 23, minutes should just go to 59, everything higher should result in recalculation of wanted time amount),
have you got 90m -> [add to final time amount] + 1h 30m calculation integrated? ^_^
With my own little unfinished calendar thingy I do recalculate everything up to years, month, days, hours, minutes, seconds, milliseconds, nanoseconds [last two only internal]
my base is milliseconds, from there I do add everything to have final time)
If that matters at all,
keep it up!
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