Clen has a long half-life also, but it hits you quick since it is a rapid-acting bronchodilator. T3 will take some time to kick in, so don't be ramping that research compound up on your rats because they aren't feeling anything!
In your opinion, is it wise to split this dose twice during the day?
Everyone has their own method. I like to take all my clen in the AM before I train. Other people can't take it before training b/c it messes with their breathing. Also some can't take a full days dose at once without bad sides. You're going to have to find out what works for you.
As far as T3 goes, I can't advise you on that one. I don't use the stuff...