As gimel said, everyone is different and must take it in the manner that works best for them. When I was on 10 mcg T3, it did work best for me to take 5 mcg in the morning with my T4 med and 5 mcg around noon or shortly after. That seemed to help prevent my mid-afternoon crash.
There is no single correct answer to that question. A lot of people would take the 115 mcg of Synthroid along with the 10 mcg of T3 at one time in the morning. Others would split the T3 and take half in the morning and half in the early afternoon. Some people even find that it works for them to take all their thyroid med at night before bed. So my opinion is to always take it the way that seems to work best for you. With the relatively small dose of T3 I really don't see the need to split the dose at present; however, as your T3 dosage is increased as needed to relieve hypo symptoms, you might find that you do better with splitting the dose.