Yes, Excel simply keeps overwriting the previous number if the value in a cell changes every 0.25 seconds, making it impossible to truly keep track of the minimum and maximum. Therefore, since there is no history to draw from, anything like =MAX(A1) will not function.

Using a VBA macro to check the value every second or so and update a separate cell to store the new max or min if it's higher or lower than previously is one approach to deal with this. An alternative is to log every value into a column or list, then apply =MAX() or =MIN() to the entire range. A little more setup, but certainly possible.