About to enter University - can I take more than one full time course? What is the usual time slot for a full time course?

Congratulations on your conditional acceptance. Contact the advising office at Plymouth and talk to an adviser about what courses you will be taking when you are there and what your potential schedule for attendance could be. Unlike high school your hours spent in the college classroom will be only a small fraction of your study time. You will be expected to do a LOT of work out of class, especially reading and writing. Arrange with the adviser to join study groups so that you have some structure and support and aren't out there on your own with potential for some big mistakes. As for your final year in HS, go talk to the high school counselor about what a reasonable academic load could be for you, allowing yourself some time to socialize as well as to fulfill the requirements for entering the program you want at Plymouth. Don't decide this on your own or with advice from strangers on the internet. Get the counselor that knows the teachers and you to help you make a decision that will work best for you. Best wishes for your happiness.

Full time means Lectures every day. You take these all together, lectures on each subject., unless your conditional offer says otherwise.
You really must research this properly before you accept.
UK