Battle time becomes a serious concern as you approach the top tiers of TH7. The giant/healer strategy starts to become too slow against many well-designed bases.
It's important to find out where you're spending your time. You can watch the replays and count seconds to get a pretty accurate picture of what's happening.
Probably the most critical parts are drawing out the clan castle troops and dealing with walls. Even a big pack of Giants still takes time to break through walls, and when many walls stand between you and your goal, things can slow down significantly.
The clan castle is important to draw out no matter what troops you're using, but you can be attacking another part of the base at the same time, if you're confident in your clan castle drawing skills. This sort of divided focus can be hard to manage, so practice it against matchmaking bases outside of war until you get the hang of it.
As some have said, air attacks can be faster, as air units bypass walls. This gets expensive, though, and it requires training to understand the best way to deploy air troops. All dragon attacks are usually so costly that you won't profit in terms of elixir from wars. However, if you're late TH7, you might not care about elixir, and you might just be in wars for the DE/gold for walls. If that's the case, then by all means blow elixir on dragons. A mix of dragons and balloons can be cheaper, and if you deploy them strategically it's possible to 3* a lot of different TH7 bases this way.
Also, you can bring along wall breakers to speed up the wall destruction process for your ground troops. This becomes somewhat difficult against bases with deep walls, as the breakers don't have much HP, take decent troop space, and are useless against things that aren't walls. If you've got a very "honeycomb" base you're up against, though, they can be devastating if used properly.
- Watch your replays and figure out where that time is going
- Learn to manage clan castle troops quickly
- Try different strategies - more air or wall breakers, for instance
- Practice against similar bases outside of war so that your strategy is honed and you can consistently deploy it properly