Does Reiatsu Crush have a specific operating speed? So it spreads passively, but how long does it take to reach the range?
So far, I have not come across a versus match where the speed was not equalized and the reiatsu was not restricted, but if you still ask my opinion :
I don't think we can talk about a constant speed value, it is probably assumed to be comparable to the attack speeds of characters in battles (if there is an accepted calculation for a general value regarding the rate of spread of reiatsu, I do not know of it).
Before Reiatsu reaches his opponent, if the opponent is faster, can he reach the characters in the bleach?
As far as I remember, some Bleach characters suppress their reiatsu in order not to harm those around them, for example, in the beginning, Kenpachi was suppressing his own reiatsu and thus his power through his eye patch, and Yamamoto suppressed himself as long as he did not engage in a serious battle, but we saw that Stark did not suppress his reiatsu and passively killed his hollow friends around him, in the same way, especially Aizen. As we can see most clearly in the 3rd fusion key, he does not hesitate to erase those around him with reiatsu (even though the range of reiatsu is restricted in the Tybw key).
Coming to the question, although it probably depends on the character you use in battle and the character's key and mood, for example, if you are using Aizen, the speed at which reiatsu spreads does not matter much because Aizen never holds back his reiatsu, so if the opposing character starts close enough to him, it will be instantly erased or if it is further away, it may affected by other effects of reiatsu.
However, as I said, reiatsu must of course have a spreading speed, and if the speed in the battle in question is not equalized and the opposing side follows a battle tactic based on run away or fighting from a distance using the advantage of range, there is no need to resist the effects of reiatsu.