It should be "0.5 amperes" and "0.5 hours". It is a rule in English that for any value other than 1, the units should be written in the plural form if they are being spelled out. If you are using abbreviations for units, however, they should remain singular in spelling (e.g. "0.5 A" not "0.5 As").
From the arguments that we have already seen, it seems to me that there is no 'correct' answer. If you follow the rule that the grammatical number of the verb is determined by the grammatical number of it subject, then the verb should be plural, whether the measure be the bucketful or the litre. If you follow the rule that there is a special exception in ...
If the sentence said "5000 litres of water ..." we would know exactly how much water is meant and would have in mind that specific volume rather than its 5000 notional component volumes, acceptably referring to it as a singular (a volume).
However, a bucket is not a defined quantity in the same way that *gallons or litre are defined. The statement ...
Normally the adjective form of the nationality is used:
Sometimes the noun form can be used instead. This is usually done when the adjective form is substantially longer than the noun form (or otherwise hard to say). Singaporean adds two syllables to the noun form and so is a likely ...