All the data for your schedules should be kept stored in the central schedule--not on individual workstations. Is the central schedule a filemaker database? If so, it should be hosted over the network and your clients should connect to it to find the schedule records that apply to them.
When searching records by date--assuming the date is entered in a field of type date--you can enter find mode and enter the dates in this format: 1/1/2010...1/31/2010. On systems that use MM/DD/yyyy format, that finds all records from the month of January of this year. You can build such requests in scripts as well if you want to automate the search for records in a given date range.