Classic now has heal prediction events and api functions thanks to recent Blizzard changes, unlike retail it currently doesn't give incoming hots (retail gives the next tick only and there is no way to change this). I expect blizzard will update the api functions to include HoT's, with this being the same as retail in a future release. Meaning only blizzard events and api calls will be supported and HoT's will only show the next tick.
The latest classic releases (era and tbc) of HealBot is using both blizzard's events/api and HealComm. HealComm is only used for HoT's and the change to 1 tick was in preparation for future Blizzard changes that will force this.
As a side note the main HealComm github source was taken down some time ago, I expect that was due to reduced support for HealComm now heal predictions are available from Blizzard, but as I have stated it seems HoT's are not yet included and so HealBot will continue to use HealComm for the time being with the change to mimic the retail api.
Have to wait until blizzard fixes the bugs in the current classic api for incoming heals to be sure, fully expect it to work the same as retail and retail only shows the next tick.
There is no option to specify time when using
Also as I stated, it seems support for healcomm is being reduce, it has already been removed from github and I expect this is due to incoming heals now available using blizzard's api.