Five minutes, measured: how long filter changes really take
Web filters rarely change instantly, whatever the brochure says. We timed ours in the lab: about 5 minutes on and 5 minutes off. The method is below, with what it means for planning a lesson.
Access reached the computer4 min 46 s to 5 min 22 s
Access was removed after its end time4 min 48 s to 4 min 50 s
A computer moved between rooms1 to 2 min
Waiting for the changeFastest to slowest of five runs
Filtering products often use the words "real-time" and "instantly". We'd rather publish numbers, so we measured ours.
What we tested
On 3 October 2026 we ran two tests in our lab on a Windows computer with the DNS Agent installed, with a typical school filter in place.
- Starting: we allowed a blocked site for a room and timed how long it took to open on the computer.
- Ending: when the allow ended, we timed how long it took for the site to be blocked again.
We ran five full cycles and didn't force anything. No restarting the agent, no manual refresh, nothing a teacher couldn't do.
What we found
| Change | Time it took, over five runs |
|---|---|
| Access reached the computer | 286 to 322 seconds |
| Access was removed after its end time | 288 to 290 seconds |
| A computer moved between rooms | 1 to 2 minutes |
In plain terms: about 5 minutes on, and about 5 minutes off.
Why it isn't instant
The DNS Agent checks for new rules every few minutes rather than being pushed each change the moment it's made. That's a common design, and it's why "instant" claims deserve a second look. It's also why the timing is so consistent: the ending times in our tests sat within two seconds of each other.
What it means in a classroom
- Allow it as the class walks in. By the time everyone has signed in, it's usually ready.
- Use lesson sets. Saving the sites a unit needs means one action at the start of the lesson, not five.
- Trust the Starting state. DNS Angel shows Starting until access is actually live, rather than pretending it's ready.
- The end is just as dependable. Access is removed about 5 minutes after its end time, every time, and the record shows when.
Questions worth asking any vendor
- How long does a change take to reach a student's computer?
- How did you measure it, on what devices, and when?
- Was anything forced, like a restart or a manual refresh?
- What does the teacher see while they wait?
We think a school deserves straight answers to all four. These are ours, and the rest is on how DNS Angel works.