Hi Rebecca,
Thanks for posting this new idea for SDL TMS. At this time, we're not considering making TM download available on demand as it could have serious implications on the performance of SDL TMS for other users of the system at the time. TMs can run to millions of translation units which would take considerable processing power to export which is why such an export is typically scheduled during quieter hours.
Having said that, the SDL TMS TM Maintenance tool can be used to do a live export of the TM but again it's worth considering the impact on other users of the system before undertaking such action.
Regards,
David