Those isometric pauses will never feel longer than they do on leg day. Trust me: you're going to want to rush through the pause and avoid the pain, but it's essential that you hold the positions for a full three-count every time. Use your partner's voice to keep you accountable and help you maintain the proper pace. Tell your partner what you need him or her to say to you. That's what they're there for.
Remember, pausing "midway" on most of these moves doesn't mean stopping at the top or bottom—that's where you're resting! In the case of the standing calf raise, for instance, you'll begin at the top, drop all the way down, start back up, and then pause. After you complete the isometric hold, continue the rest of the way up to the starting position.
The trick to making the most out of these isometric lifts is to find the spot where feel the most tension on your muscles. It's going to hurt, but you can handle it!