SSDM-13524: Fixed timestamp parsing logic

...thz/sis/openbis/generic/asapi/v3/dto/dataset/DataSet.java

.../generic/asapi/v3/dto/dataset/create/DataSetCreation.java

...is/generic/asapi/v3/dto/dataset/update/DataSetUpdate.java

...s/openbis/generic/asapi/v3/dto/experiment/Experiment.java

...ic/asapi/v3/dto/experiment/create/ExperimentCreation.java

...eric/asapi/v3/dto/experiment/update/ExperimentUpdate.java

...z/sis/openbis/generic/asapi/v3/dto/material/Material.java

...eneric/asapi/v3/dto/material/create/MaterialCreation.java

.../generic/asapi/v3/dto/material/update/MaterialUpdate.java

.../ethz/sis/openbis/generic/asapi/v3/dto/sample/Sample.java

...is/generic/asapi/v3/dto/sample/create/SampleCreation.java

...nbis/generic/asapi/v3/dto/sample/update/SampleUpdate.java

.../server/asapi/v3/helper/generators/AbstractGenerator.java

...neric/server/asapi/v3/helper/generators/DtoGenerator.java