Update Rationale (ethereum#5154)

EIPS/eip-5133.md

@@ -24,7 +24,7 @@ fake_block_number = max(0, block.number - 11_400_000) if block.number >= FORK_BL
 ```
 ## Rationale
 
-The following script predicts the bomb will go off at block 15530314, which is expected to be mined around mid-September. This gives reason to address because the effect will be seen, but not so much urgency we don't have space to work around if needed.
+The following script predicts the bomb will go off at block 15530314, which is expected to be mined around mid-September.
 
 ```python
 import math
@@ -44,6 +44,9 @@ def predict_bomb_block(current_difficulty, diff_adjust_coeff, block_adjustment):
 print(predict_bomb_block(13891609586928851, 0.1, 11400000))
 ```
 
+Precise increases in block times are very difficult to predict (especially after the bomb is noticeable).
+However, based on past manifestations of the bomb, we can anticipate 0.1s delays by mid-September and 0.6-1.2s delays by early October.
+
 ## Backwards Compatibility
 No known backward compatibility issues.