To the best of my understanding, there is no formal announcement date for each tender tranche. Some are more complicated and need more consideration than others, for example
a) where TFL tender multiple options - in terms of route, frequency, vehicle types or any combination of these (and the route options may need considering in the light of any consultation exercise)
b) where operators offer multiple options, e.g. we will do route A for X price, route B for Y price, but we can do routes A and B for Z price. And / or alternative prices for new / refurbished buses / electric / hybrid buses.
And if a route falls in to both categories, or if routes A and B are in different tender tranches, then it gets more complicated.
This is TFL bus tendering page and does include tender results - although as of today, tenders awarded on 18 May are the latest shown, while LOTS has those awarded on 20 June (albeit just showing who the winning operator is.)
Broadly speaking, operators who have won / lost / retained routes are advised (at high level) in confidence the day before the tender award is made public, then all operators are advised the results of all of that day's awards the next day at which point it's considered to be in the public domain.
I'm not quite sure who else is on the circulation list, LOTS seem to get it fairly quick. Presume the info is posted on TFL's website fairly quick, but doesn't seem to be a press release as such.