GABA type A (GABAA) receptor is a ligand-gated chloride channel which mediates fast inhibitory signals through rapid postsynaptic membrane hyperpolarization whereas the metabotropic GABAB receptor produces slow and prolonged inhibitory signals via G proteins and second messengers (GPCRs).
As far as drugs go, Diazepam and Alprazolam are examples of agonists that bind to GABA A and do so quickly whilst Gabapentinoids like Baclofen or Phenibut bind to GABA B and may take hours to kick in yet GHB is also an agonist there but kicks in must faster.