Let’s take the facts of Ravi Prakash Singh v state of Bihar, (2015) 8 SCC 340 for the purpose of illustrating. Here are the brief facts:

• Accused first surrendered before the Court on 05.07.2013 and 1^st remand order passed is passed on the same day. 
• Bail application filed by the accused on 03.10.2013 on the ground that he is entitled to default bail as 03.10.2013 was the 91st Day and chargesheet not having been filed in 90 days, the right has accrued.
• Police-report/chargesheet also filed on the same day i.e 03.10.2013.
• As per the police, chargesheet was filed within time as 03.10.2013 was the 90^th day. 
• As per the Accused, 03.10.2013 was the 91^st day.
• The Court held : The Accused was NOT entitled to bail as the chargesheet was filed on the 90^th day.
• The Court held that while computing period under Section 167(2) proviso of the CrPC, the day on which accused was remanded to judicial custody (i.e 5.7.2013) has to be EXCLUDED, and the day on which challan/charge-sheet is filed in the court (i.e 3.10.2013), has to be INCLUDED. 
• In other words, 6.7.2013 is the first day (from which the counting has to start) and not 5.7.2013 and so counted, 3.10.2013 is the 90th day and not the 91st day.

Further readings/sources:

• Section 167(2)proviso – CrPC.
• State of M.P v. Rustam and Others, 1995 Supp 3 SCC 221
• There is a contrary view also in old judgments and, recently, the Bombay High Court decision in Kapil Wadhwan v. Directorate of Enforcement, LDVC Bail Application No. 400 of 2020 – where the Court took a contrary view and held that the date of first remand has to be included while computing period under Section 167(2) CrPC. (relying on some older SC judgments.
  • PS: The last I checked the operation of this order was stayed by the SC.
  • PSS: Recently, in ED V. Kapil Wadhwan & Anr. (SC: Criminal Appeal No. 701-702 of 2020, decided on 23rd Feb, 2021) the issue was referred to a larger bench.