timely; opportune
Timely help
Untimely/ill-timed/mistimed/inopportune remarks
To arrive at an opportune moment/at the right moment/at the right time/at the proper time/in due time/in proper time/in the nick of time
To turn up like a bad penny/at the wrong moment; To come at an awkward moment; To come amiss/inopportunely
Just at the moment when....
She greeted me with a nod just at the moment when I was brushing my teeth
Just at that moment; at that very moment; at the very same time
At that very moment, they burst into laughter