No, it doesn't matter, because you choose an agitation regime that gives you the results you want.
Also, the importance of small variations in agitation is commonly exaggerated. The difference between minimal and constant agitation is equivalent to at most a change in dev time of about 15%. From this it is not hard to see that the difference between 10% agitation (6 seconds/minute) and 20% agitation (12 seconds/minute) is unlikely to equate to more than about a 5% change in dev time, e.g. 30 sec. in a 10 minute dev time. From personal experience over 40+ years I'd say it was actually a good deal less than that.
Of course you need to be as consistent as possible, but (as with most things in photography) it is all too easy to become obsessive and to look for an accuracy that is not there and cannot be brought to the process.
If you want more accuracy, one of the most useful tricks is to take the temperature of the dev as it goes in, and when you drain it out. This may convince you of the importance of a water bath. It's also worth remembering that precisely because plastic holds the heat better, it also takes longer to warm up/cool down and has a greater thermal capacity, i.e. a warm or cool tank will have a greater effect on the temperature of the dev. than a stainless one.
Cheers,
R.