Thank you for your reply. I am a beginner in Quantum physics and I am both amazed and perplexed with the double slit experiments. So theoretically the delay can even span for years and the interference pattern will still emerge.
I have one last question: in the same double slit experiment...
In a 'one photon at a time' double slit experiment, does the interference pattern still emerges if the time delay between individual photon emissions is increased to minutes or even hours?