Hi,
In the Fluorescent Light preset, there are flicker effects on the individual letters and the whole word itself.
Click on the text layer a type UU. That will bring up all the properties that have been used to make the effect. Under RANGE SELECTOR 1, you’ll see keyframes for OFFSET that go from -15 to 100. Bring those keyframes closer together to make the individual letters flicker faster and more often or farther apart to make it slower and less often. As far as the whole word flickering, under WIGGLER SELECTOR 1, you can change the WIGGLES PER SECOND to suit your needs.
Also, you can change what flickers-the character, word or whole line under the BASED ON properties.
HTH,
Jim