@Trevor.Dennis, Nope, I've tried with no luck. The total is 12 seconds but in two sequences, while I want 8 seconds in a "single sequence" to run simultaneously without changing the speed of two animations.

You mean like this?
The text animation runs on 2s and the blinking one runs on 1s (base frame rate of 24fps). The animation is actually slightly longer than 8 seconds. As was stated before, the blinking consists of only 6 frames, and two frames at the very end will have to be cut off to match the frame length of the text animation.
I did this in OpenToonz - easier to do in OT, since importing the two gif animations automatically creates two frame-based timelines, and the text anim is imported on 1s. With OT I selected those frames, and told it to expose on 2s. Then repeated the first 6 frames of the blinking, and exported as a gif animation.