Constructor to set a particular expiry time as an absolute time.
template< typename ExecutionContext> basic_waitable_timer( ExecutionContext & context, const time_point & expiry_time, typename constraint< is_convertible< ExecutionContext &, execution_context & >::value >::type = 0);
This constructor creates a timer and sets the expiry time.
An execution context which provides the I/O executor that the timer will use, by default, to dispatch handlers for any asynchronous operations performed on the timer.
The expiry time to be used for the timer, expressed as an absolute time.