Most old schoolers could switch to splits in as little as 4-6 weeks. Once the 4-6 weeks adaption process with TBT 3x a week, had occured the switch could be achieved.
Stagnancy of the TBT system, depends on 2 things. How the body responds to a specific format of TBT I.E. the chosen exercises sets, reps, plus how diet affects things. Smaller factors like water, sleep and hormone secetions, come into play.
TBT can be made more challenging by going for close ot max lifts and alternating workout setup ever 3-6 weeks, though I say, if a programme keeps working stick with it if you like, as often the a plateau has little to do with a schedule that the body has adapted to, but a lack of caloric intake, so plateauing would be better served sorting out diet before consiering training changes as oftne people flit from one adaption to another, sometimes potentially wasting up to maybe 2-3 months, before considering diet to be the key to further progress.
There are 3 things to consider weith TBT and splits.
1. Don't overload with weight.
2. Don't use sloppy form or technique.
3. Don't waste time with pissy or physically risky exercises, like Wrist curls or behind the Neck stuff, that may place risk on certain joints or tissues, or simply waste time utilising less muscle fibres than other exercises.
One main difference is thart with Splits you either do a 5 day one, a 3 day one, where you double up area, like Chest / Triceps for example, or you do a 4 day one, Upper, Lower, Upper Lower.
Some say TBT allows you to train again before atrophy occurs, because of the timeframe between workouts, but others prefer the higher volume splits will allow and think the growth potential in relation to the atrophy betwen individual body part workouts, is not significant to cause a stunted progress effect, allowing you to really work the specified area more throughly, with a mix of compound and more isolatory style exercises.
Eother / or will do, it's just a case of if you wish to stay on TBT or go to splits and if you choose splits would you go for a 3,4 or 5 day one. Providing you don;'t do the 3 aforementioned things, you won't have any real issues with injury risk, or shouldn't whatever training style you use.