Hi Ryan,
Thanks for contacting Syncfusion Support.
You need to call Measure() and arrange() method of chart manually before saving. If it is done then you can save the chart even if it is not in the UI. Moreover, we have verified in our side it is not taking more than a second.
We have attached a sample for your reference and it can be downloaded from the below link,
Please check the above sample and let us know if you still face any problem with this.
Regards,
Durgadevi S