I may have missed shkiah by a matter of seconds. I remembered I needed to do a hefsek tahara, looked at a clock connected to digital radio (i.e., very accurate) and it said 5:28 then raced into bathroom and did it without washing. It only took less than a minute. But shkiah is listed on the internet as being at 5:28. We live in Sydney in the east. Not sure where they calculate from, i.e., east west altitude, etc. What to do ???? Thank you. Without rabbinic approval I'll just wait another day and be really annoyed with myself.