I've had a single entry Chinese visa and visiting Guangzhou for 5 days.

Alex, you don’t need to apply for an entry permit to HK because Indonesia passport holders can enjoy free entry to HK for a stay of no more than 30 days.
But if you will come back to Guangzhou after you’re one-day travel to HK, you will need to re-apply for an entry permit to re-enter mainland PRC because you currently hold a single-entry one.