Are you actually or do you just "feel" like you are? Assuming you're referring to running (since that's where your question is located)
Some people prefer to workout in the evening and have more energy for it. If you run outdoors, it may be cooler or lower humidity, which could help your performance (e.g., I run slower when it's real humid because it negatively impacts my breathing).
If you don't actually run faster, but just 'feel' like you do, it may be your mental attitude in the evening is more confident and energetic, than earlier in the day.