Which message boxes?
If you are referring to (for example) inputdlg() then it forms a modal dialog and waits to be closed; the only way that you could have something start itself executing in order to command the closing of the dialog box would be if you used a timer().
If, though, you use msgbox() then by default it does not create a modal dialog, You can use delete() on the handle returned by msgbox() in order to remove the msgbox() dialog.
