So much (mis) information here, some good some bad.
First, the TDI's glow system operates
at every start from ambient temps on any day of the year in any state or province in North America. Yes, you read that correctly. Your car sat overnight in August in Florida, guess what? When you start your car up, the plugs get powered up.
Now, for how long (both for the pre-glow and post-glow) depends on coolant temp and RPM.
The indicator in the cluster is NOT an indicator of whether or not the plugs are powered up, but an indicator of when the system says you can start the engine. The plugs may remain powered up, under 2500 RPM, for several minutes... longer periods in the cold.
This is normal. This is called afterglow, post glow, or whatever, and is intended mainly for smooth running and lower emissions during warm up. Older (pre-TDI) VAG diesels did not do this. Their post glow was about 3 seconds, and once the relay clicked off, it stayed off.
Pre-2002 TDIs have their glow plug relay in the inside of the car, in the relay box, and it is normal to hear it clicking on and off as the car warms up. Every time you sweep over 2500 RPMs, it clicks off. Then back on again when it sweeps below 2500 RPMs. It will do this until the coolant is up to a temp predetermined by the ECU's programming that says "OK, the engine is warm enough, we can keep the plugs off". 2002+ cars placed the relay outside the car, near the ECU (on Golf/Jetta/NB) and under the coolant bottle (on Passats) and they are actually a slightly different functioning relay (duty cycled) but that is not important right now.
If you feel your preglow period is somewhat short, meaning the time the light stays lit, you *may* have a faulty coolant temp sensor that is not giving the correct value to the ECU. So, if it is 25 F out, and your ECU is getting a signal that it is 75 F, the preglow will be shorter than ideal. But since 70 F is within the normal range of the CTS, the ECU will not flag this as a fault.
While you can electronically lengthen the preglow period with VCDS or similar on many cars, keep in mind these items:
1:
some light smoke on a cold start and during warm up is
normal It is even stated in the owner's manual.
2: improper timing of the pump, a worn pump, poor injector spray pattern, poor fuel, weak compression, etc. can also cause some excessive whitish smoke after a cold start.
3: a weak battery can also cause excessive smoking, as not only will the engine not crank as fast as it should, the glow system will be placing a massive drain on it both before and after the starter has done its job, further increasing smoke as the electricity to the plugs is reduced and they won't get as hot as quickly.
I have started countless TDIs up cold, have owned them from new all the way to nearly 400k miles, VEs and PDs, and they should all start right up down to single digit (F) temps without too much drama. However, they are all going to put some puff of something out the tailpipe. It may not be enough to see every time, but standing behind the car you'll see
something and again, this is normal.