Worked it out now
When you start composing your email, press "save" to start the "Autosave" routine. When on return later you needn't touch this the process carries on Automatically And you can always override the autosave clock by pressing the save button if its not greyed out(for a short time afer it autosaves)
PS Google should rename the key "Autosave" or "Save-Start" on a later update as thats what it does