Some Questions about the daily prayers

Hello everyone, Al Salamu 3alaikom wa rahmat Allah.
I have a few questions regarding our daily prayers.

Firstly, when I was young my mother and father taught me how to pray, as I grew older, I had to memorize the tashahud. My mum would give me a small piece of paper to read off during the prayer but since I had to learn it, I was bit quick about it and had some reading problems reading, My arabic was weak at the time.

Now, I have recently found out that very small sections of the tashahud that I recite in the prayer are incorrect, or are not supposed to be there.
For example:
"Atta-hiyyatu lillahi was-salawatu wat-tayyibatu As-salamu 'ala an-Nabiyy wa rahmat-ullahi wa barakatuhu"

My version would read:
"Atta-hiyyatu lillahi was-salawatu wat-tayyibatu As-salamu 'alaika ya Rasool Allah wa rahmat-ullahi wa barakatuhu"

I have been praying this way for over 6-7 years. Now that I have realised this, I've changed, but will God not accept my prayers from before?

The above is just a small example listed there are 2 others, small not large changes, but nonetheless they are still changes.

I have another question regarding the morning prayer, or the first prayer to start off the day. I haven't necessarily prayed this morning prayer on time, since I haven't considered setting an alarm to wake me up. However, I do wake up at about 5:30 to go to school, once I do, I take a 10-15 minute shower. Once I have made Ghusl, what's the latest time that I can make this prayer without it being considered disliked in our religion? Since according to what I know, a Muslim must always make sure he prays on time.