It's not a dumb idea and it doesn't have to be covert. However, it's a low percentage choice for your first race weekend as you'll be plenty busy just doing the basics of staying relaxed and driving the car well. You probably don't need to focus on lap times just yet. (Unless you've been highly competitive in karting or other racing already)
Check out these threads
http://www.teamjuicyracing.com/forum...ighlight=timer &
http://www.teamjuicyracing.com/forum...ighlight=timer for info on two different brands that are commonly used.
I use the Ultra-Lap timer and many also use the AIM timer. They both use the same frequency for their start/finish line beacon. (Don't know compatability of their split beacons)
You tape the timer screen to the RT windscreen and tape the small receiver on top of the car bodywork facing the side of the track with your beacon. Place your beacon on the pit wall or a tripod and point it across the track. The timer reads the beacon and reports accurate times to hundredths of a second. With multiple beacons splits can be recorded but I've not seen any situations where skippy racers have actually used them. (Though we have bantered it about in the threads)
Because we share and frequently change cars, putting a timer on and off is an added nuisance that is probably more trouble than its worth to a first time racer. If you are a return visitor to a track it can be helpful in knowing where you are in relation to your last visit. It can also be useful during qualifying to let you know if you've reach your target time or not but again, I wouldn't even think about that if you are racing for the first time.
Look or ask around at the track and I'm sure someone will show you their's and demonstrate it if they aren't busy.
In the first few lapping sessions that I carried a timer I taped over the screen so I couldn't see the times until I was out of the car. It's nice to have the times after the session but I still rarely look at it while driving because I find processing the information, in most circumstances, to be an unwanted disttraction.
I recall an instructor saying that they actively discouraged new racers from using lap timers (viewable in the car) because, in their experience, it only led to trying too hard and crashing.