Spending two days in a lab can easily save you up to one hour reading literature

Following: a few pre-formulated responses to common, questionable design decisions and typical problems.

This is a canned comment to let you know that it looks like you're trying to implement something that is non-trivial with the power-hungry NE555 but is very easy for someone using a microcontroller.

This is just a canned comment to let you know that what you're trying to build from discrete analog components (possibly incorporating Opamps and/or NE555) is a digital control problem and thus can easily and with lower parts count be solved with a microcontroller with really minimal firmware to write.

I'm voting to close this question as off-topic because OP has bought a device from a supplier that doesn't supply a datasheet. Device doesn't work as expected for application. Since no guarantees made by a datasheet can be expected, there's nothing to answer here: Get a device that comes with a datasheet that guarantees operation under the conditions that you need.