After a bit of deliberation, came up with the following as The Most Critical Times at Shiloh:
4:55 a.m. First contact. (Some record this time as 5:15, probably due to watch error.)
9:05 Brigadier General Prentiss retires with most of his artillery (and the sturdy bits of his infantry) to what will become the Hornet's Nest.
10 a.m. The "key time" for General Sherman: after meeting with General Grant, things start to fall apart on the Union Right.
2 p.m. Buell arrives at Pittsburg Landing and meets with Grant (despair caused by "no reinforcements" evaporates, replaced by Hope.)
2:30 Colonel Webster begins assembling Grant's Last Line (from all available artillery.) General Albert Sidney Johnston dies.
5:29 The exact time recorded by General Prentiss that he, and those stalwarts with him, surrendered.
6:25 p.m. Sunset. General Beauregard calls a halt to offensive operations.
Can you think of any other times on Sunday 6 April 1862 more deserving of inclusion on the above list?