1. Loading the file
The file loading process will take some time depending on the file size, presence or absence of additional elements in it (macros, etc.) and the connection speed.
2. File conversion
The file is being converted into Office Open XML format for the document faster viewing and editing.
3. Loading editor scripts
The scripts for the editor are loaded only once and are will be cached on your computer in future. It might take some time depending on the connection speed.
Please note, that the speed of all operations greatly depends on the server and the client locations. In case they differ or are located in differernt countries/continents, there might be lack of speed and greater wait time. The best results are achieved when the server and client computers are located in one and the same place (city).