Latest juice from Dahua France support page.
http://supportfrance.dahuasecurity.com/firmwares/DH_NVR5XXX-4KS2_MultiLang_V4.000.0000001.5.R.20191218.bin
Dahua Toolbox includes Disk calculator. The amount of time depends of bitrate and if the recording is constant or by motion/alarm.
http://www.dahuasecurity.com/support/downloadCenter/tools/maintenanceTools?path=window
Close Chrome browser
remove c:/Program Files/webrec and c:/Program Files (x86)/webrec folders
reinstall plugin
There are so many different Dahua Webservice plugins, that it generates problems sometimes - then just get rid of them and start over.