function watch(~, ~, time)
Note that this will always give you the same time. When you create a callback such as [@watch,clock()} then those arguments are evaluated at the time the callback is constructed, so the time of callback construction is what is going to be recorded in the callback.
You should consider,
sec = timer;
set(sec,'ExecutionMode', 'fixedRate', 'TimerFcn', @(varargin) disp(datetime()));
start(sec)
