First, you don't want append , you want appendcols . When you use append , you will end up with multiple events - you want all these results in a single event.
Second, you need to time-constrain your inner search, else it runs over all time. I have done that by using addinfo to collect the time parameters of the outer search, and then apply them to the inner search.
Finally, I don't think you need the final stats command, either.
specific.server
| stats dc(userID) as totalUsers
| appendcols [ search specific.server AND "text"
addinfo | where _time >= info_min_time AND _time <=info_max_time
| stats count(field) as variableA ]
| eval variableB = exact(variableA/totalUsers)
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