You can avoid using the colon and employ ISO 8601 basic format strings (YYYMMDDHHMMSS) or a variant for naming files and folders. If you need to process those strings with certain programming or scripting languages then maybe you have to convert them to the extended format that incorporates separators (hyphens, colons) and time zone info.
International standard date and time notation - "If a date and a time value are stored together in a single data field, then ISO 8601 suggests that they should be separated by a latin capital letter T, as in 19951231T235959"
