Snodmaulvenn... In general it is best to keep the Fortify Animations and Sounds to around 1/2 a second... especially if the Unit has Multiple Attacks.
IF a Unit has Multiple Attacks, best to keep each Attack short, about 1/2 a second. If each Attack is Long the Game will not play them back correctly... some or all will be shortened.
If a Unit has a Very Long animation for the Attack, you can split the animation into 2 or even 3 parts = Attack A, Attack B and Attack C. The Game will play them without hesitation so it all appears as one long Attack procedure.
An example of this is My Unit, The Drunk. It uses all three Attacks for just the One long Attack that I split into 3 parts. You also will need to split the Sounds to fit each Attack Part.
You can take a look at the Original Game Units to see that they tend to be short animations and sounds.
You can get away with some longer animations and sounds but in general it is best to try to keep Animations and Sounds for Unit Attacks to 1 second.