When to think about adding more yeast to fermenter

[NWMushroom]

I brewed an all grain porter recipe on July 24th. Today there is still minimal airlock activity (I know that's not a real measure of fermentation) so I took a gravity reading and it hasn't budged from the OG of 1.050.

There does seem to be a layer of CO2 pressure in the bucket as if I tap on the lid, it kicks the airlock into releasing a few bubbles.

I used a 1l yeast starter on the stirplate so it was tough to tell viability. It was on the stirplate for around 20 hours before pitching. Pitching temp was 75 degrees, starter temp was 73 degrees. Yeast was WLP004 Irish Ale. The wort is currently sitting at 68 degrees.

The recipe and yeast was shipped from Austin Homebrew Supplies. My concern is the yeast may have got damaged from the heatwave (no ice pack selected).

So my question is: when should I expect to see the gravity reading drop on a hydrometer? Should I just bite the bullet and do the 2 hour round trip drive to my 'local' homebrew store and pick up some more yeast to pitch?

Thanks in advance.

 

[Shooter]

Personally, I've never had a yeast take longer than 48 hours and even that is rare, normally some activity is happening within 24. However, some people have gone as long as 72 hours before something started happening. I'm assuming you don't see any krausen forming yet. However, CO2 pressure building in the bucket seems to indicate it's doing something. Could be it will take off at any point now. I always have an extra packet or two of dry yeast on hand, just in case there is an issue, but that doesn't do you much good at this point.