Hello alexaugusto1!
We appreciate you reaching out to us!
Sure, it's possible. We can use
formatter function for that and over there define what should be displayed inside the tooltip.
Demo:
https://jsfiddle.net/BlackLabel/2p73edgw/
API references:
https://api.highcharts.com/highcharts/data.dateFormat
https://api.highcharts.com/gantt/tooltip.formatter
Let me know if that was what you were looking for!
Best regards!