It can be hard to tell, and that's why you might consider testing for structural breaks or statistical visualization methods of the series you're examining, in addition to narrative accounts. For the Tequila crisis, it broke around December 20th 1994 and may have ended around March 10, 1995 (the GAO report might be the best for details http://www.gao.gov/products/GGD-96-56 ). For the Asian Crisis, see Kaminsky and Schmukler's "What triggers market jitters? A chronicle of the Asian crisis." JIMF 1999. I used their dates in a paper I wrote; their chronology of the Asian crisis and Russian default crisis includes four phases. They list July 2, 1997 in Thailand as the beginning. I found that growing problems in Thailand were evident a year before the crisis (this is consistent with narrative accounts given by traders, who said they knew there were problems before then). Early February 1999 is when the crisis seems to fizzle out in Latin America (although Argentina had a follow up crisis see Yeyati, Schmukler and Van Horen's Ec Letters paper http://siteresources.worldbank.org/DEC/Resources/LevyYeyati-Schmukler-VanHoren-ADRsandCrises.pdf ). For the Dot Com bubble, see Jeremy Siegel's "What is a Bubble?" article in the European Journal of Finance DOI: 10.1111/1468-036X.00206 . For the Global Financial Crisis, there are probably lots of time lines out there, but try the St. Louis Fed for a start https://www.stlouisfed.org/financial-crisis/full-timeline . I don't know as much about the sovereign debt crisis literature, but I'm sure there are some good chronologies out there.

 Dear Naveed Raza 

Greetings,

Yes I agree and support what  Stephen Matteo Miller ·said .

Best Regards

check the data sets in eichengreen(various), the crisis data set in imf , and the detriagache and demirguc-kuntz dataset

https://www.imf.org/external/pubs/cat/longres.aspx?sk=26015.0

Dear Naveed Raza

There is no fixed date for any financial crises. But it is very much known to politicians and capitalists as they are the people who plan the crises for the benefits. World bank, IMF and other financial Institutions and other national banks are indirectly controlled by the capitalists and they with collaboration with politicians chalk out the plan and gradually implement it and which transformed into financial crises.  

Try some variations on my graphed search trends, linked below.

https://www.google.co.za/trends/explore#q=%22Mexican%20peso%20crisis%22%2C%20%22Russian%20crisis%22%2C%20%22Asian%20Financial%20crisis%22%2C%20%22dot-com%20bubble%20burst%22%2C%20%22Sub-Prime%20crisis%22

Dear Dr. Naveed Raza, 

Greetings,

Yes I agree and support what  Stephen Matteo Miller said two times too!.

Best Regards

Bashkim