Nathan....unless you running it constantly, and I mean constantly, through the pipes all morning and again all afternoon you will probably get about 66% of the tank temperature the rest will be lost in the hose length especially if your running 100m of it at this time of year over cold ground.
It will take a good few minutes at start up on morning and afternoon to reach said temperature so you will either have to start off cleaning with cold water or wait.
Depends on what you put the flow rate to but if you want it hot on start up you will waste a fair bit of water.
I use 60c hot water for carpet cleaning and over say a 20m run first thing it can take 90 seconds or more to get up to a decent temperature and that's hose run indoors not outdoors.
60c for cleaning carpets is northing we use 270c and at the wand jets it I around 250ish at 500psi
all so you can lose heat quicker if using a four jet wand or brush (window cleaning) its well know in the c.c. trade that the single jet wands hold the heat better , so I guess it will be the same for window cleaning two jets better then four where heat is used
270c ? 
something for you to read gob poope
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