The key to your success would be the streamstats command. I am not sure if it is the most pretty or effective solution, but it gives you the wanted results:
| streamstats count as opencount by Open_date
| streamstats count as closecount by Close_date
| timechart span=1d max(opencount) as "Tickets opened", max(closecount) as "Tickets Closed"
Your data needs to have the event timestamp as the creation day for this search to work, maybe you need to tune this a bit by adding an eval _time= .... to your search to achieve this.