[plt-scheme] Timedeltas for PLT?

Hi,

I am trying to write some small non-trivial programs in Scheme and
while looking for stuff that might help me I ran across PLT Reference
Chapter 14.6, Time, <http://docs.plt-scheme.org/reference/time.html>.
Now, I'm quite used to Pythons datetime
<http://docs.python.org/dev/library/datetime.html> which has two
constructs that are useful to me: datetime.strptime and the timedelta.
Is there something like this also for PLT or do I have to create my own
library[1]? 

regards,
Marek

[1] that I could upload to PLaneT if it proves useful