"By this time" means "now that we have reached this point."

In Arabic, we typically say something like بحلول هذا الوقت.
For example:

By this time, all the birds have gone back to the north.
بحلول هذا الوقت، تكون الطيور جميعاً قد عادت إلى الشمال

Notice that a significant part of the meaning is dependent on how the sentence is constructed, and a significant part of that is the word تكون or يكون. If you take that word out, the meaninag evaporates.

In some legal contexts, the expression اعتباراً من الآن may convey the meaning. For example:

By now, all employees are expected to have completed their training.
اعتباراً من الآن، نتوخى أن يكون جميع الموظفين قد أكملوا تدريبهم

The example you cite is interesting in that the simple word الآن may suffice. For example:

By this time , you all know me.
الآن قد عرفتموني جميعاً

This is one more example of how time references are much more difficult to express in Arabic than in English.