2. On holidays and at weekends the exchange rate increases, therefore the best time to exchange currency is on working days (from Monday to Friday) during business hours, moreover, the rate is normally lower in the morning and in the evening it tends to increase.
This is due to the internal work of banks which calculate the rate based on the currency market quotes. Trades on the currency market are held in the morning which is the basis for setting the official exchange rates by banks.
Which is why you may face a situation where in the same bank on Saturday you will get less rubles for 200 euros than you got for the same amount on Wednesday. It is not an intentional deception but an increased spread.