I visited a month or so ago and it wasn't at that time. Maybe contact the museum directly for up to date advice?

Not sure I understand your question. We entered through Chambers Street. I believe that is the main entrance. There is access to the entire museum from that entrance. Seems we went up some stairs from entrance and that took us to the main multi story room. From there all the exhibits and rooms were available.

Hi, The National Museum of Scotland is based in the centre of Edinburgh and we do not have on-site parking. The Museum is a 10-15 minute walk away from Edinburgh Waverley train station. More information on city centre parking and transport options are available on the main website.

We want everyone who comes to our museums to enjoy their time with us and make the most of their visit. There is level access to the Museum via the main doors to the Entrance Hall on Chambers Street and the Tower entrance at the corner of Chambers Street and George IV Bridge. Four designated public parking spaces are available for disabled visitors in Chambers Street. There is no charge for these spaces. However, please note that they cannot be booked in advance. Wheelchairs are available for loan at no charge. Please note wheelchairs cannot be booked in advance. On arrival, ask about availability at the Information Desk. Small mobility scooters are permitted inside the museum. Lifts are available to all floors and there is a variety of seating throughout the museum. Accessible toilets are also available on most floors and there is a Changing Places (U) toilet in the Entrance Hall on Level 0. You can download a map of the museum to see the exact locations of our lifts and accessible toilets. We hope you enjoy your visit!

Unfortunately, I cheaped out and didn't go in to that. Based on what I could see and size wise, I would guess at least an hour if not two.

Admission to the National Museum of Scotland is free, although donations are welcome and are increasingly critical to enabling us to continue our work. If you would like to visit one of our major exhibitions, tickets cost around £10 for adults (free for Members).

I’m sorry I don’t know, I’d assume guide dogs would be allowed

We went on a hot day. It was not fully air con and felt a bit stuffy but not nearly as bad as outside. Lots of enclosed areas to keep cool