Every winter our Hibiscus plants get hit hard. It takes this long for them to revive, even here in Florida. I am always amazed at how precise mother nature is with flowers.
The type of hibiscus you have is one that cannot take frost or freezes well. It will die back to ground in winter and will come back if mulched good where it goes below freezing to 20 degrees but won't bloom till August and that depends on full sun, fertilizer and lots of water. If you will keep it in a pot in the winter where it is protected from freezing it will start to bloom in April or if in house in sunny window will bloom summer and winter. happy growing and remember it likes regular feedings I use 20.20.20 same as peter's professional at the rate of l.4 tsp to gal of water and do so at every feeding especially in a pot.