How Long. At bare minimum, your warm-up period should be five minutes long. If you are practicing an intricate sport like gymnastics or ballet, you need much longer than five minutes to properly warm up. Also, when your muscles are extremely sore from a previous workout, you will need to take more time to warm up. In general, aim for a five to 10 minute warm-up period before any workout. Flex this time frame up as needed, but never skip it. Also, do not abbreviate your warm-up to less than five minutes.