How long have you been together as a couple?
You should cover the entire length of your relationship, but you shouldn't send more than 1-2 sheets of paper showing messages.
So, if you've been together 6 months, you might send the date and time of 2 messages per week. If you've been together 2 years, you might send 2 per month. If you've been together 5 years, you might send 1 per month etc.
All you are showing is regular communication - just that you have stayed in contact during the length of your relationship without any large gaps.
If you have visited each other, then evidence of the visits (boarding passes) will supersede the messages, so you show the messages from when you've been apart.