How long should a toast message with ‘undo’ appear?

In our application, the user can make small changes, such as deleting a chart from a report.

When they delete an item, a toast notification appears to say "Chart 2 was deleted successfully. Undo?"

The undo option makes it easy to quickly recover from errors. But how long should the message appear, before it fades out?

Currently it is set at 60 seconds. But that feels way too long, especially as hovering over the message, even during the fade, suddenly resets the timer.

Note that the message can also be cancelled with an 'x' and multiple messages get stacked, blocking any underlying content.