What clients can see

Your clients only see what you've invited them to see in the portal, and even then only finished, billable work. Nothing is shown while it's happening.

What a client sees of your time

A time entry appears in a client's portal only when all of these are true:

It's for that client.
It's finished. A running timer is never shown. If you resume a stopped entry, it leaves the portal until you stop it again.
It's billable. Non-billable time is left out of the portal and its totals.
It's on a project that's shown to the client (see below).
The project isn't internal. A project set to Internal — never billed is never shown, whatever its visibility setting says.

Time with no project is never shown until you file it under a shown project.

For each entry the client sees the project, date, who did the work, the description (and memo, if you use one), and the billed hours. Entries never show rates, amounts or costs. See What your clients see in the portal for the rest of the portal.

Show or hide a project

Every project is shown in the portal by default.

Open the project.
In Details, tick or untick Show this project in the client portal.
Click Save.

The badge at the top of the project says which it is: Client can see this or Hidden from client.

a project's Details card with the portal checkbox and the visibility badge

On an internal project the checkbox is greyed out: internal work is never shown to the client.

What hiding a project does

Its entries disappear from the client's timesheet, their recent work and their export.
Its time still draws down the client's hours, so Hours left in their portal can go down without matching entries in their timesheet.
It isn't offered in the portal's project filter.
Its files leave the client's Files page, even the ones marked Shared, and no email announces new ones. They come back when you show the project again. See Share files with a client.
If you send statements of hours, its billable time that used the client's hours is still listed on them, by project name. So is billable time with no project. A statement accounts for every hour taken from the balance.
On invoices in the portal, lines for that project still appear with their amounts, but the project's name isn't shown.

Nobody sees anything until you invite them

A client has no portal access until you invite someone from the client's People tab. See Invite clients to the portal. Contacts who only receive invoices can't sign in.