The possible dates in which the sale of Steam will take place have been filtered and, as you imagine, it is very close.
What happens is that Pavel Djundik, member of the Steam Database, assured that the Steam summer sale will take place from June 25 to July 9. This means that the offers will last 2 weeks.
Now, it is important to note that, for the moment, Valve has not said anything about it. So, although the information comes from a good source, things may change.
As usual, we will be pending and we will inform you when we have more information about it. We will also notify you once discounts are available.