Looking at the code in Code.xs

void
DateCalc_Add_Delta_DHMS(year,month,day, hour,min,sec, Dd,Dh,Dm,Ds)
    Z_int       year
    Z_int       month
    Z_int       day
    Z_int       hour
    Z_int       min
    Z_int       sec
    Z_long      Dd
    Z_long      Dh
    Z_long      Dm
    Z_long      Ds
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sorts of indicates why you can't use fractional parameters. ;-(

If you really want, you could write a routine that would take fractional day, hour, minute and second(?) parameters, and put that subroutine "in front of" the existing subroutine. A sort of non-object oriented subclassing ;-). Or, if you are sure that your "day", "minute" and "second" fields are always 0, use your solution:

print join(" ",Add_Delta_DHMS(Today_and_Now, 0, hms(1.1));
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but I would find that pretty yucky and poorly maintainable.

Hope this helps.

Liz