Hi Matthias,
Thanks for using Syncfusion products.
The cell tooltip delay duration can be changed using the AutoPopDelay property. Please make use of the below code,
Code Example
//To set InitialDelay and AutoPopupDelay.
this.gridGroupingControl1.TableControl.CellToolTip.InitialDelay = 100;
this.gridGroupingControl1.TableControl.CellToolTip.AutoPopDelay = 1000;
Sample Link
Regards,
Amal Raj U.