You can do it like this:
handles.tb=uicontrol('style','text','position',[200 100 200 40]); %create a textbox
for i=10:-1:1
handles.tb.String=sprintf('Start in %d',i); %change string of textbox (2013 or older matlab versions require different synthax)
pause(1)
end
The time between each number decrease will be a few milliseconds longer than 1 second though.
