I believe your client is wrong. To help persuade him, you could point out that as is it parses like a list of three items:
- "value matters"
making the reader think What are "value matters"?
You want it to be a rephrasing of
"When time matters, quality matters and value matters, count on TEAM."
But when you put the three things in a list you need to use the plural form, "matter", not "matters", like "All of your needs matter to us".
For an alternative, I'd suggest this, which I think is a nicer way to get across the meaning that time, quality and value are all equally important:
"When Time, Quality and Value all matter – count on TEAM."
Here, "all" clarifies that what is different about TEAM is that they give equal importance to all three of these things (the three things which you can never achieve at once according to the classic "development triangle").
I've also taken out all of the unnecessary capitalisation, except for that on the three key components you're trying to emphasise.