Gardening Question ?

[Tarragon2017]

Ok I potted up my herbs using the same compost , and it rained today. How is it some of the compost still feels damp at 8pm considering it rained at 930am , whereas some herbs soil feels drier.

As a general rule shall I wait till the top layer is dry till I water again. Even for water loving herbs such as coriander , and Vietnamese coriander and Basil

Thanks