Firstly, the unit of timeout is milliseconds, so 45 seconds translate into 45000 milliseconds.
Secondly, since the script already provided 5 seconds delay, you need to delay it further for another 40 seconds (40000 milliseconds) to get a total of 45 seconds.
Finally, the code:
setTimeout(function(){
require(["mojo/signup-forms/Loader"], function(L) { L.start({"baseUrl":"mc.us11.list-manage.com","uuid":"32e8df9557dd399bb3ba2ae61","lid":"6d35f0128b"}) })
}, 40000)