For instance, the disintegrating time of core tablet is 5 minutes, but after coating, disintegration time increases to 10 minutes. This mean the disintegration time of tablet always increase to double after coating.
It is not surprising to have an increment in the disintegration time since there is a coating (could be sugar or film) on top of the core tablet. Additionally, lubricants are also known for their DT prolongation, but I am afraid to say the mean DT always doubles after coating. check this out on the details of DT tests for different types of tablets: http://www.pharmacopeia.cn/v29240/usp29nf24s0_c701h.html
Once the core tablet is coated, an increase in disintegration time (DT) is expected; however, the extent of the increase is not fixed and does not necessarily double. In the case of standard film coating, the DT typically increases by only 1 to 2 minutes, unless a high-viscosity polymer or PVA-based coating material is used, which can lead to a more significant rise in DT.