Heating mixture and pure substance question!

[Nisou]

This isnt a homework question, just something i was wondering while flipping through my chem textbook, i was looking at a chart and it shows the heating process of both pure methanol compared to 75% water and 25% methanol

 

when pure methanol is heated, it just starts going up and a pretty uniform rate.. but when the mixture of water and methanol is heated, it goes up slowly for around 2.5 seconds.. and then starts going up much faster than pure methanol, why is this?

 

is there a.. building-up-energy time or something when heating up mixtures, or is it only in this example? thanks in advance =)