Possibly what you write is what I mean, but I understood from your writing, that the 45s delay is more like the tubes wait for the solid state to be ready than the opposite?
1-2 minutes tube soft start time is also what I’m used to. No problem with waiting as long as I don’t need new tubes every 1-2 years (as I use little more expensive ones)
By googeling I find something like this under „tube soft start“:
Is something of this happening in the BHK for tube sake?