It is possible to create a Fraction in two ways,
either "now" with no arguments or
from a unix time (as from time(2)).
If created from unix time, both the start of the period
and the size of the period can be given in floats,
both representing seconds. Note that the default
float precision in pike is rather low (same as 'float' in C,
the 32 bit floating point precision, normally about 7 digits),
so beware that the resolution might bite you. (Internally
in a Fraction, the representation is an integer.)
If created without explicit length, the fraction will always be
of zero length.