Slow start with yeast starter?

Brewed up a a white IPA yesterday. It is my third time making more or less the same recipe. First batch didn’t ferment down as low as I liked (stalled at 1.017). Second batch was money. I wanted to remake what I made that second time.  All 3 batches I made a yeast starter (WLP 400). I used roughly a 1.2L starter of 1.035 wort. The ONLY thing I did differently, was I added some yeast nutrient to the starter during its 15 min boil. I had an insane amount of activity in my 2L flask while on a stir plate. I usually some sanitized tin foil to cover the top of the flask. It was so active that I did have some krausen spilling down the sides, but nothing major. Starter went for roughly 16 hours ( I usually go 20-24 hours). I pitched the yeast to my 70 degree wort yesterday at 2. We are now 27 hours later and I see no activity. How worried should I be? My bucket is in a chamber at 70 degrees.
Yeast production was 3/27 and I used MR.Malty’s calculator for viability.

Give it time and check the seal on your fermentation chamber-it could be leaking. It will take off.

+1.  Bet it is already fermenting and you just don’t know it.

My chamber is a 5 sq ft chest freezer so the seal is good there. I double checked the lid on the bucket and pressed down. Seal seemed fine there too. We shall see. I do have it connected to a blow off tube so maybe it will take some more time before I notice bubbling in the bottle where the tube goes to. I just don’t remember it taking this long the past 2 times I brewed this beer with WLP400

this has happened to me many times. I think I have a stalled fermentation… low and behold it’s almost done.