mixpanel.time_event $duration not showing on my events

hello, 

I am using mixpanel.time_event as outlined here https://developer.mixpanel.com/docs/javascript-full-api-reference#mixpaneltime_event

my goal is to see how long the Analyze process in my electron application takes. 

I expect: the $duration property to be attached to my mixpanel event ‘Analyze’ when it completes to simply see how long it took from start to complete. 

Issue: the $duration property shows for when the ‘Analyze’ event starts, which is pointless because I dont need the time from the time_event to the start point, I need from the time_event to the completion point. 

• the $duration property does show when my mixpanel.track event is completed in the mixpanel user activity feed and only shows for when it starts not when it completes  
   

I start the time_event when the user presses the button ‘Analyze’ as such on the renderer side(front end): 

		mixpanel.time_event('Analyze');

		var mixpanel_log = Object.assign(
			{
				type: 'system',
				status: 'success',
				reason: 'analyze server start',
				data: data_to_clean
			}
		);
		mixpanel.track('Analyze', mixpanel_log);

and then I have another mixpane.track when the Analyze process completes, in a different component in my electron app on the main(backend) side, as such. 

		mixpanel.track('Analyze', {
			type: 'system',
			reason: 'complete',
			specs: specs
		});

both of my tracks show successfully in the activity feed on mixpanel, the only thing missing is the Duration when the event actually completes.