Scheduling a text to send later is very easy. Open a message, input the recipient and on the text line, to the left, click the arrow to expose the camera/pic icons and hit the + beside them. Under there, you will have several options, and one is scheduling to send later.
Hi userGC3wCbZX01, thank you for reaching out, and I am sorry you are unable to locate where to add a text signature or schedule texts. I can certainly understand the convenience of these options, as well as the personalization of one's texts. What phone are you attempting this on, what Android version, and what messaging app are you using?
Scheduling a text to send later is very easy. Open a message, input the recipient and on the text line, to the left, click the arrow to expose the camera/pic icons and hit the + beside them. Under there, you will have several options, and one is scheduling to send later.
