4.2. Time-based Contract.19 This type of contract is appropriate when it is difficult to define the scope and the length of services, either because the services are related to activities by other for which the completion period may vary, or because the input of the consultants required to attain the objectives of the assignment is difficult to assess. This type of contract is widely used for complex studies, supervision of construction, advisory services, and most training assignments. Payments are based on agreed hourly, daily, weekly, or monthly rates for staff (who are normally named in the contract) and on reimbursable items using actual expenses and/or agreed unit prices. The rates for staff include salary, social costs, overhead, fee (or profit), and, where appropriate, special allowances. This type of contract shall include a maximum amount of total payments to be made to the consultants. This ceiling amount should include a contingency allowance for unforeseen work and duration, and provision for price adjustments, where appropriate. Time-based contracts need to be closely monitored and administered by the client to ensure that assignment is progressing satisfactorily, and payments claimed by the consultants are appropriate.

4.2 Ugovor koji se temelji na roku.15 Ova vrst ugovora prikladna je u situacijama kada je teško utvrditi djelokrug i duljinu trajanja usluga bilo s razloga jer su usluge vezane uz djelatnost drugih osoba i za čiju cjelovitost može biti različito vremensko razdoblje, ili stoga što je unos savjetnika potreban za postizavanje ciljeva radne zadaće teško procijeniti. Ova vrst ugovora se naveliko rabi kod složenih studija, kontrole gradnje, savjetodavnih usluga i većine radnih zadaća koje uključuju školovanje. Plaćanja se ugovaraju prema satu, dnevnici, tjednoj isplati ili temeljem mjesečnih obroka za osoblje (koje se obično u ugovoru imenuje), te prema nadoknadivim točkama uporabom stvarnih troškova i/ili jediničnih cijena o kojima je postignut ugovor. Obroci za osoblje uključuju plaće, društvene troškove, naknadu (ili zaradu) i tamo gdje je to primjenjivo posebne nagrade. Ova vrst ugovora uključuje maksimalni iznos sveukupnih plaćanja koja se daju savjetnicima. Platni iznos uključuje kontingencijsko davanje za nepredvidive poslove i trajanje posla, te provizije za prilagodbu cijena, gdje se to smatra prikladnim. Vremenski ograničene ugovore stranka mora oštro nadgledati i administrirati kako bi se osiguralo da radna zadaća zadovoljavajuće napreduje, a plaćanja koja savjetnici zahtijevaju odgovaraju činjenicama.

http://hrvatska.poslovniforum.hr/nn-arhiva/0004f/04f4f.asp

No idea if there is any "standard translation", but this is the meaning.

time-based contracts = you get paid (some agreed hourly/daily rate) depending on the time spend on the task , as opposed to a contract where you get paid a known total amount (fixed in advance).

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Note added at 7 days (2019-02-20 15:36:03 GMT)
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unless you find some shorter widely accepted term meaning exactly that (I can't think of any), this is a perfectly usable variant.