How many minutes does a sundial change every day? I'm planning to create a sundial in Ghana (10° 28.852', 0° 26.032') in July 2014.
I will stay there for about 3 weeks.
Do I need to adjust the numbers anywhere in these 3 weeks?
I know the shadow's path changes through the year, but how much does it change?
Is the change significant for a sundial?

(btw, is this the correct site to ask or should I use the astronomy site?)
You need to look up "the equation of time" - this is a correction to the time reported by the sun on any given day - the apparent solar time - (and measured by your sundial) and the standard civil time - the mean solar time - it varies throughout the year and the maximum your sundial will be out is about 15 minutes - but the difference and the rate of change varies. http://en.wikipedia.org/wiki/Equation_of_time

If your sundial is merely for educative/demonstration purposes, this might not matter so much of course - as the sundial will surely demonstrate that the sun's shadow can be used to tell the time.