PhotoRead the answer keys as well. It add to the mind processing the rest of the information, why make it hard on yourself? Sometimes when you read the answer you spend a lot of time pondering how they got the answer and where it is. That gets worked at an other than conscious level of the mind anyway so why delay it?
It's not cheating. The answer key wouldn't be there if it didn't help to add understanding to the material.
If you only have 30 minutes a day you can use the techniques from the 5 day test (page 76 of the PhotoReading book) on your textbook. You purpose might be to understand the material, section by section day by day. If you apply the 5 day test and treat each subject as a book. Then within that time you would have done a very detailed study of that material.
Alex