What the meaning of "bottom" referred to a time period

In the sentence

A lasted till the bottom of B

where B is an event which, in its turn, lasted some years, "bottom" is the beginning of B or the end of B?

I found it in an economic article, the actual sentence is

the regulatory wave lasted till the bottom of the world 2007-2009 crisis

(Henry Penikas, "History of Banking Regulation as Developed by the Basel Committee on Banking Supervision in 1974-2014 (Brief Overview)", 2015).

From Investopedia

A bottom is the lowest price reached by a financial security, commodity, index or economic cycle. Often, a specific time span is used to determine a bottom, and that timeframe can be a year, month or even intraday.

In your case “bottom” refers to the worst phase of the 2007-2009 economic/financial crisis