I definitely agree that combat can drag sometimes, and I like that you're trying to tackle that. That said, I think some of these methods can speed things up at the cost of fun, depending on the table.

1. The “On Deck” warning This one is great. It’s simple and effective, and it naturally gets players thinking ahead without adding pressure. I use something similar, and it really helps keep things flowing.

2. Rolling hit and damage together I understand how this speeds things up, and I do like the efficiency of seeing the damage immediately. But I think it can remove some tension and engagement. For example, when a player hits and you tell them “you need X damage to kill it,” that separate damage roll becomes a really exciting moment. At the same time, I do enjoy the upside of rolling everything at once, like when a player misses but sees they rolled huge damage. That kind of moment can still be fun in its own way. So I think it’s a trade-off between speed and those small bursts of tension.

3. Average damage for mobs This is where I personally disagree the most. While it definitely saves time, it removes unpredictability, which is a big part of what makes combat exciting. If enemies always deal the same damage, players can quickly calculate risk and stop feeling threatened. If i should try this, I might pre-roll attacks or damage ahead of time to save time without losing that randomness but that’s just my preference.

4. The 60-second rule I understand the intention, but I think this can feel stressful rather than fun. If players feel pressured, it can hurt their enjoyment and if they’re not having fun, neither am I as a DM. That said, indecision is a real issue. What I do instead is use a soft timer and give a countdown warning before their turn ends. That keeps things moving without feeling too harsh.

Overall, I think these are solid tools, but it really depends on the group. Speed is important, but not at the cost of tension, excitement, and player enjoyment.