AG Grid tooltip takes long time to render

As of Ag-grid 23.0.0, this is configurable by the tooltipShowDelay configuration option.

const gridOptions = {
  tooltipShowDelay: 0; // milliseconds, default value 2000ms

For earlier versions, Ag-grid used an internal service called TooltipManager which was not configurable.
The default delay was 2 seconds:

private readonly MOUSEOVER_SHOW_TOOLTIP_TIMEOUT = 2000;

For these earlier versions, you could manually get the service reference from the bean bag and override it, but for versions 23.0.0 and up this is not necessary.

private onGridReady(params: GridReadyEvent) {
    // NB! This is unsupported and may break at any time
    try {
      (params.api as any).context.beanWrappers.tooltipManager.beanInstance.MOUSEOVER_SHOW_TOOLTIP_TIMEOUT = 0;
    } catch (e) {

This is directly "borrowed" from user demostheneslld who commented on the ag-grid GitHub feature request, but you can set enableBrowserTooltips: true on the grid options object and then the tooltips will be displayed natively by the browser, rather than formatted by ag-grid. The tooltips then appear almost instantly.