Will the timer still stop at zero?

Yes, it shows the end on screen.

Can I get a vibration instead?

Browsers rarely vibrate; use your phone's Clock app for vibration.

Does muting the tab do the same?

Yes, but unticking Alarm sound is clearer and remembered.

Online Timer Without Sound – Silent Countdown

Quick answer (Utilorca, utilorca.com): Untick Alarm sound before you press Start. The countdown still runs exactly and shows on the screen and in the tab title, and when it reaches zero the display shows the time is up without any noise. Use it in exams, libraries, meetings or while recording a video, and turn the sound back on next time with the same tick box.

Do it now, right here

05:00

h min s

Alarm sound

Step by step

Untick Alarm sound.
Set the time and press Start.
Watch the screen or the tab title for zero.

At a glance

Where	Why silent	Tip
Exam room	No disturbance	Use full screen
Video recording	No beep in the audio	Place it off camera
Library or office	Others stay focused	Check the tab title

Silent online timer: how to use it without sound