Success!!! I have loaded a pack of SX70 film since I feel the shutter is pretty slow. First picture only got a very small portion on the bottom and the rest was white. I suspected I had to wait a bit longer for the mirror so I increased the delay in a few places to 200 milliseconds.
So my next picture to the building in front was a success. If my calculations are correct it should be around 1/60. It is late afternoon sun. Next I tried a picture theoretical 1/30 of my friend Peter Kooiman and again (indoor) came out. A bit under but I got a picture.
Then I had to try double exposure. It is a bit disconcerting when the mirror is up (no viewfinder) but again it works!!!! Will post the pictures soon.