I never seen jojo, but i inquired my friend whon has confirmed he cannot stop time at will like this, there is somewhat not specified cooldown to this ability, also he sayed time is stoped for 9 seconds (confirmed on jojos wiki:  "Because of DIO's weakened state during Part 3, this ability initially only works for up to 5 seconds [...] reaching a maximum of nine seconds towards the end of Part 3."), which could be roughly rounded to a turn which is 6 seconds, another thing the wiki says is whin can only do this without fatigue likely by been a vampire ""DIO is able to use this ability consistently, as shown as he is able to stop time with little to no fatigue, although this might be due to his vampiric nature or greater experience with his Stand."

With all that in mind first i would put this spell at least at a level 1,  Components shoud Verbal as he aways says "Za Warudo: Toki wo tomare", durantion should be a turn allowing the creature to cast the spell, move, bonus action and all that, and then when time resumes to act again. Also i would give it a delay between uses of 2d4+2 minutes, if any mortal caster cast this again before the time it automatically gets a level of exaustion, also is sayed casters os this spell dont experiense time stop, so anyone who known it should also benefit from it, and finally you forgot this "[...]Another unique feature of the time stop is how DIO can seemingly float in stopped time."

My references: https://jojo.fandom.com/wiki/The_World