There is no easy way to know how long something will take.

The thermbar is your best bet if you can update it as you go along.

Here is some (edited) code I used before to do something similar

loTherm = NewObject("_THERMOMETER","_THERM.VCX","","Output All Pages")
loTherm.Show()
loTherm.iBasis = RecCount("loadedhtml")
Do While Not Eof("loadedhtml")
	loTherm.Update(RecNo("loadedhtml"),"Outputting page: "+allt(loadedhtml.directory)+allt(loadedhtml.file))
	**** do stuff
	EndIf
	Skip in LoadedHtml
EndDo
loTherm.Complete()