the sun - 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?)