Yeah, like Lex says but also add a timer. For example you want these two messages to fire in order when a hoplite reaches a healing spring:
Trigger: AAA
Condition: Units is Area
Effect: Message #1 (fade out 4000 ms)
Effect: Fire Event (Trigger BBB)
Trigger: BBB
Condition: Timer (6 seconds)
Effect: Message #2
Those two triggers will fire message 1 when the hoplite reaches the healing spring, and six seconds later message 2 will appear automatically. Notice message one lasts for 4 seconds, there is a second for it to fade out, then message two fires. Be careful with the length of the message and the timer for the next one to make sure they don't overlap or that the incoming message doesn't cut off the prior one. This is only one way to set up a timer as others exist. You can chain as many messages as you want all triggered by a single condition. Just repeat the fire even in the prior trigger and a timer in the following trigger.