There is a lot that can be discussed here from the perspectives of mechanical turbulence, thermal turbulence, and shear turbulence. To cover all that in context of a dynamic site like Lookout, would take books of information, which would most efficiently be presented via conversation- in fact many many conversations and only to really understand you need to fly often at the site. However, I will take a stab at a very very generic explanation specific to your question of why that when there are east winds (which is an entire different discussion b/c your statement of "east winds" is incredibly simplified when in reality there are at least 2-3 dozen factors/hazards involved with "east winds") in context of why after 11am. Others should chime in here, if so inclined.
Firstly, 11am is just a general rule of thumb and it all depends on the season on day's conditions. 11am in winter is different than 11am in high summer. So, do not use 11am as a hard and fast rule on when conditions are getting out-of-hand, rather it should be how the conditions are developing. Now, onto your question of conditions after your 11am timeframe, or 9am, or 2pm- it's all relative per my above comment.
Very generally speaking, thermic conditions develop (get stronger) throughout the day (from dawn) until peak soil heating occurs at around 2-3pm (assuming no atmospheric interference, such as clouds). The sun’s maximum zenith is noon, but soil sorption of the sun’s shortwave radiation lags by 2-3 hours. Thereafter, thermal conditions begin their path toward weakening, although very strong conditions can, and often do, persist until the early evening- so again, it's all relative on that day's conditions. During that timeframe of mid to late morning and mid to late afternoon, thermal strength increases, often times dramatically at locations like Lookout. With increased thermal strength and maturity, thermal turbulence generally linearly increases (barring other factors such as inversions, caps, wind shear, etc… again, another conversation). For newer pilots, and the old dogs alike, conditions can surpass the skills of the pilot leading to dangerous flight configurations.
The "east" wind you mention is a completely separate matter (upslope induced flow regime on the lee side of a mountain range) than why it's discouraged for newer pilots to fly mid-day conditions at Lookout and in fact at every other thermic site out there. So, what I've talked about here deals with the thermal turbulence part of the equation. Lookout, given its aspect, altitude, setup to local flow patterns, and physical makeup, often yields outstandingly dynamic conditions that can quickly become challenging for any pilot. That is why there is a 10-flight sponsorship program, which helps pilots start their journey to understanding the site. While construction in the LZ is occurring (check other forum postings), the sponsorship program has been put on-hold, for safety reasons.
Hope that helps, a bit.
, ) jake