When is a deadline of Sunday 3rd July 2016, 2400 hrs (GMT) [closed]

This isn't technically for travelling, but I would imagine travellers may have the same issue sometimes. I am doing a essay for a competition which states the deadline is "Sunday 3rd July 2016, 2400 hrs (GMT)" Is this early Sunday morning or Monday morning? Or to put it another way, is this late Saturday or late Sunday? I want to know so I can work out if I have Sunday as well to complete the essay ;)
I've seen this on stack exchange: https://stackoverflow.com/questions/13060467/difference-between-2400-and-0000 Which got me to this wiki article: https://en.m.wikipedia.org/wiki/24-hour_clock#section_1 But it doesn't really help because it suggests that 24:00 is equivalent to midnight, but in this ambiguous case it still isn't clear if they actually mean Sunday midnight, or if they are mixing two ideas, where '2400 hours'='Saturday midnight' but they wrote Sunday thinking '2400' represents the earliest morning time possible. This is very confusing so I hope my question is clear!