In general, IMHO, the question, as already noted above, is formulated incorrectly. There is a whole set of factors, such as: the size and composition of the army, the number of magic points (both yours and the enemy's), the number and quality of the enemy's spellbook, and which SPECIFIC creatures are part of the armies (living, undead, or dead). Also, it is necessary to consider the possibility of using a double spell after waiting. In general, there are many things to consider. Heroes is a game where every little detail matters. :)