When I use a countdown timer in instant message, can I increase the size of the text? I usually insert a blank slide, with a background of course, insert a countdown timer and 'hide' 'unhide' as needed. I would like to add text above the timer like Worship Begins In. How do I do that?

At the bottom of the countdown creator page, there are two sliders for text size, one for the text and one for the timer. A little crude, but it works OK.

I assume you're talking about Improv Collection -> Instant message. That's what we use.  Clear to the right of the improv collection pane is < Settings < (vertically). Click on that and you'll have all kinds of adjustments.  This takes some experimenting. 

For the message I use Service starts in {countdown to "next half hour" format "m:ss"} You can type the text, then use the "Insert" dropdown to insert a live date, time or countdown.

I use a black bar at the bottom of the screen, The placement is set to Left 0%; Top 90%; Width 100%; Height 10%. For the text, I use left 5%; Top 5%; Width 90%; Height 90% and white text. For container, I just use black with 100% opacity and no edge blend. 

I show this with our announcement loop, which has its bottom margin set to 10% so it doesn't cover any of the announcement slides.

I use the countdown to "next half hour" in a small box, maybe 10% x 10%, a corner of the announcement loop. Change which corner depending on the background

and just to be different sometimes.