如果不是必须，尽量避免在夏季早上10点—下午2点出去用英语怎么说

If it's not a must, try not to go out on 10 AM --- 2 PM in summer.

是错的，是中式英语，还有语法错误，must是不能用做名词的，正确的一种表达是：Avoid being outside from 10 A.M. to2 P.M. in summer if it is not necessary.

If it's not a must, try not to go out on 10 AM --- 2 PM in summer.

没错8

If unnecessary, try to avoid going out during 10 am to 2 pm in Summer.

If not necessary, avoid going out from 10 am to 2 pm in summer as possible as you can.

if you don't have to, avoiding going out from 10AM to 2PM in summer days