How long to get to White Hart Lane from Greenwich for a 3pm kick off???

[SerendipityAlways]

My DH and DS are lucky enough to have gotten tickets to a Spurs premiership game this Sunday 17 March in White Hart Lane, kick off at 3pm. We're on holidays in London that weekend and are staying in Greenwich. It seems to be a bit of a trek to get to the stadium, can anyone advise how long roughly it will take to travel using public transport to get to White Hart Lane?? (Our nearest station is Greenwich DLR) .
They're playing Fulham so I expect there will be a huge London crowd travelling and the match is a sell out.
Any local advice really appreciated as my 10 year old DS is beside himself with excitement and I just want to make sure they arrive on time!!!