The temperatures will be hot in St. Louis, as expected this time of year with lots of humidity. As a result, the PGA has allowed the greens to grow at Bellerive the past few weeks to help prevent heat-related stress. What the players have experienced regarding slowness during practice rounds this week will obviously quicken a bit during the tournament, but overall don't expect flawless, OMG speed putting surfaces. I suspect the greens will be relatively soft and receptive, at least the first couple of rounds, and despite the slower pace on the greens - I suspect the scoring will be good. You give these guys receptive greens - they're gonna score. The PGA has gotten the course setup much more right over the years for their major championship than the USGA has.
In other words, scoring conditions should be relatively good overall.
The weather forecast is also typical for the midwest this time of year. Hot and humid, with the outside chance of a thunderstorm popping up, over the weekend rounds especially. But I don't anticipate a major issue regarding the weather extending the tournament into Monday.
The link below gives the starting times/parings.
It's also worth noting that starting next season (2019), the PGA Championship will officially become the second major of the season, beginning the week of May 13th, at Bethpage Black, only a month removed from the Masters on the schedule.
More food for thought: although the odds are extremely remote, a player who goes on to win the next four majors would do so without achieving the coveted career Grand Slam, (unless it happens to be Francesco Molinari, of course).
Should be an interesting week!