How to make a boss summon other mobs/ minions?

Hello
I'm trying to make a custom mob boss that after a certain time like a minute it would summon 5 custom mob entities that attack the play? I have tried multiple ways that ended up either not doing anything, spawns hundreds at once instantly or in a minute and keeps summoning, or stops everything except the player moving and even freezes mcreator.
If anyone knows how it would be greatly appreciated if you can help
thank you