A timer in other form

It looks like your problem is about "in other form". The simplest solution is obvious: you need to have an internal method in one form and one form instance should have a reference to another form instance. This is not elegant though as a form can get more access than it's really required.

This is the popular question about form collaboration. The most robust solution is implementation of an appropriate interface in form class and passing the interface reference instead of reference to a "whole instance" of a Form. Please see my past solution for more detail: How to copy all the items between listboxes in two forms[^].

—SA