When making meringue and beating it to stiff beaks it takes around 5 minutes to beat the meringue to stiff peaks.
It can take awhile for the sugar to dissolve and for the meringue to reach stiff peaks.
But it should only take around 5 minutes of beating the meringue before it reaches stiff peaks.
If the sugar in the meringue has not dissolved fully then you still need to beat it some more until the sugar dissolves and so that it doesn't taste gritty.
Once the sugar has dissolved and it doesn't taste gritty anymore then you've beaten it to stiff peaks and it's ready.
But usually 5 minutes is enough to beat to stiff peaks which has been my experience.