In general the opening hours of the Vatican Museums in Rome are the same every day of the week. The museums are closed during sundays and religious holidays. Admission is 17 Euros, but there is a discount for students younger than 25. Their dress code says that you have to have your knees and shoulders covered.
Opening hours Vatican Museums Rome
Opening times

The Vatican Museums are opened from Monday to Saturday, from 09.00 until 18.00. The ticket office closes two hours before closing time. The Vatican Museums are closed on Sundays, except for the last Sunday of the month, when they are open from 09.00 until 14.00. On Sundays the ticket office closes at 12.30.
The Vatican Museums will be closed when the last Sunday of the month coincides with a religious holiday.
The Vatican Museums are closed on the following religious holidays: January 1,6; February 11; March 19; Easter (April 1 and 2 in 2018); May 1; June 29; August 14,15; November 1; December 25, 26.
If you buy the ticket at the entrance it is valid only on that date.
Entrance fee
Admission is 17 Euros. For children between 6 and 18 years of age admission is 8 Euros. Students younger than 26, in possession of a valid international student ID, also pay 8 Euros.
On the last Sunday of every month the Vatican Museums offer free entrance. Note that, even in the off-season, on those days it is incredibly crowded, even more so than usual.
Disabled people (in possession of a document showing that they are at least 74% disabled) with one accompanying person have free admission.
The ticket for the Vatican Museums includes a visit to the Sistine Chapel. (Note that during conclaves the Sistine Chapel cannot be visited.)
Lines at the Vatican Museums, especially during the high season, can be long. For an extra 4 Euros per person it is possible to reserve a visit through the Vatican website. This same page supplies information about booking visits for guided tours to the Vatican Museums and the Vatican Gardens.
During the summer months (except for the month of August), on Friday evenings, the Vatican Museums open from 19.00 until 23.00. Last entrance is at 21.30. A reservation is mandatory. The admission price is the same as during normal hours.
Dress Code
The dress code for the Vatican Museums is the same as for Saint Peter’s Basilica and all other churches in Rome, so make sure to keep your shoulders and knees covered. This is obligatory for both men and women. Sandals are allowed.