Yes, the clen and T3 clear fast, but how long does it take the HPA to reset for normal thyroid production? Being even mildly hypothyroid during the first trimester isn't a good idea.
I'd say 90 days minimum, why take a chance with your children. In fact, I'd probably get off the T3, wait 30 days and have your TSH, T4 and T3 uptake checked (standard thyroid panel). If all is normal, then go for it. If not, then wait.
W6