1) Can we use adverbs like today and now with present perfect
eg He has gone to USA today.
There are some adverbs you can use with the present perfect and some you can't.
Is that we never use specific time with present perfect or can we use
2) Can in one sentence there can be two different tenses. Of course
Do you read much? All of your current questions will answer themselves if you find some good reading material and read a bit every day.