Would i really need to wait 12 hours to take claritin (loratadine) 12 hour allergy medicine?

Not really: The claritin-d that is designed for dosing every 12 hours is related to the "d" decongestant pseuodoephedrine 120 mg. A higher dose is more likely to cause side effects. The 5 mg of Claritin (loratadine) could certainly be taken sooner as the usual dose of Claritin (loratadine) for >12 years old is 10 mg once a day.

Yes: Unless it has a decongestant, it is generally considered safe to take even up to 10 mg of Claritin (loratadine) 4 x a day if needed even though this is 4x the dose approved. But we do use as much as 4x the dose for those who have hives.

Not really: The Claritin (loratadine) reditab 5 mg will last about 12 hours, but there is no harm to taking one sooner or just go for the 10 mg reditab for 24 hour relief.