What's wrong with adding a simple (ish) method in Delay:-

Delay>untilMilliseconds: anInteger
	"Return a new Delay to wait until the time is the given value of
milliseconds. Sending 'wait' to this Delay will cause the sender's
process to be suspended until approximately that time."

	| delayTicks |
	delayTicks _ anInteger - Time millisecondClockValue.
	delayTicks < 0 ifTrue: [self error: 'delay times cannot be negative'].
	^ self new
		setDelay: delayTicks
		forSemaphore: Semaphore new

This would work within the same limits that the current delays work - ie
the delay is within 32bits of milliseconds. Delay>untilTime: and
untilDate: would also be possible but would require some trickery to
handle wraparound of the millisecond value etc.

tim