It is ok to start to try conceive now. Steroids
go off the system fairly quickly (less than a week), and in any case you - the woman - have not been on any of these medications.
takes much longer to get off the system, but this should not be stopped as it is a great medication to keep the Ulcerative colitis
under control, and should not give any problems in terms of achieving pregnancy
If your husband had to use steroids recently it means that his disease has not been completely controlled by only Imuran, and he should be considered for an additional medication (depending on his history). This should be addressed with his gastroenterologist.
Hope that helped.