Filter on time of day

I am trying to get the exim filter file to forward email to different
addresses depending on the time of day. Any ideas? My experiments with
above/below and tod_full have not proved fruitful.

Am I expecting too much from filter files?

Thanks

Andy
-- 
Andy Mell, Network Admin,                 Phone: 01893 359536 (ext 6353)
Cambridge University Press,                 Fax: 01223 325972
Shaftesbury Road,                         Email: amell@???
Cambridge CB2 2RU, UK.             Urgent Email: amell-pager@???