Not sure why the installer takes so long for you to open/display when you launch it. I don't think Chrome is delaying it in any way. Anti-virus might though in some rare cases.
You might want to delete everything in "C:\Windows\temp" and "C:\Users\yourusername\AppData\Local\temp" to see if the Opera installer launches right away the next time you use one.
Did you use the simple net installer (that's not very big in file size that fetches the install files from Opera's servers when you try to install) or the offline installer (that's a big file that already includes all the install files)?