Time as currency is first used in 1827 by Josiah Warren in the founded from him Cincinnati Time Store. He closes the store in 1830 reporting its success to dedicate himself to utopian implementation of his idea.
In 1973 was implemented the first Time Bank by Teruko Mizushima in Japan where the accent was on using the time invested on a later date, mostly for social services, because of his expectation that the japanese society will age.
In 1991 the idea of using time as a currency comes in the USA, and in 2002 Timebanking UK is founded - a national chartered organization with own exchange for services like cleaning, video editing, it services etc.
Currency (The transformation problem)
The transformation problem (see https://en.wikipedia.org/wiki/Transformation_problem) is the question how to convert the worked time into consumer prices (value, see https://en.wikipedia.org/wiki/Labor_theory_of_value) in the conditions of a market economy. (See Marx)
The use of time as a currency transforms the problem upside down, reducing it to Value = Time.
In other words we can reduce any product or service to the invested time capital (working hours) in its production. As Adam Smith observes - a diamond has no value until somebody bends down to pick it up from the ground. The so defined Value lead us to the consequence, that "profits" should be a part of the in any product or service invested human time.
Usage to date
In its modern variant (see timebanking.org and timebanking.org.uk) time currency is mainly used as a medium for barter of services. As already mentioned the main idea behind this is the organizing of social groups, which support elderly, needy and other interested individuals. Seyfang reports, that time banks promote social inclusion and help the integration of socially excluded persons (see https://appropriate-economics.org/materials/time_banks_rewarding_community_self_help.pdf)
Here we propose that the physical resource time be implemented as an universal currency available to every member of the human race for the exchange of as of services so of goods. The aspects and needs of the so used time currency and its comparison to the now used currencies will be researched in following articles.