Of course! Your page will continue to accept donations even after you've reached your target. Please note we minus our fees of 2.9% +0.25p from the amount raised before transferring the funds, so you might want to factor this in when setting your target.
On average, people who hit their target do so after just six days, which leaves plenty of time to raise as much as possible. If you hit your target mid-way through the project, increase your target and then add an update to let people know how the extra funds will be spent.