Hisashiburi is strictly used to note that is has been a long time since a person last did something. When person A says to person B, "o-hisashiburi," it means "I haven't seen you in a while," "I haven't written to you in a while," "I haven't talked to you in a while," etc. "Hisashiburi-ni Nihon ni ikimasu" means "I am going to Japan for the first time after a long time." On the other hand, "shibaraku" denotes a short period of time. It means "for a moment" or "temporarily" For example, "shibaraku kokode matte kudasai" means "please wait here a moment." Hope this was helpful.