You should've decided if the 'title' is already visible or not, at the beginning of the animation. For this and for its 'on' & 'off' states:
- double-click the desired layer
- on the upper left side of the layer properties panel, on General tab, there's a checkbox for "Visible"
If unchecked on frame 0, the layer will be invisible during the animation. When you need it to be seen, place the playhead on the desired spot on the timeline and - double-click the layer and on l.p. panel check Visible. The layer will be visible from that point on, till you uncheck it.
Each time you change the state of visibility a keyframe is created on the timeline, for that layer. Once you have these keyframes, and if you need it to be some sort of a flashing neon sign you may:
- copy-paste them where you need them again OR
- right-click on the last keyframe and choose Cycle from the dropdown menu.
This should open a Keyframe panel where you may adjust the cycle towards your preferences but also a rectangular 'arc' would appear above the keyframes (on the timeline) for that layer depicting the span of the cycle (which frames are repeated). After a few tryouts, I'm sure you'll figure out which settings would fit the bill.
This method works like a light switch with the simple on/off states but if you use 'Opacity' instead or even combined, you may achieve some dimming effect as well. This largely depends on the sign's design since for this effect to be convincing you'll need to find a proper length of the switching sequence, you'll need some background behind the sign or some other nearby surface to receive the reflected light, you might need to divide the sign into a couple of layers if there's some outline on it.... etc. Again, a few tryouts would be necessary till you fine-tune it but this should be worth it, especially during these festive days