The word ‘day’ may be qualified. In particular, although the effect of custom may be to restrict the meaning of the word ‘day’ to those days upon which it is customary to work, lay time may be expressed in terms of a number of ‘working days’. Indeed, prudent negotiators of charterparty clauses will not leave such things to chance and will include a reference to ‘working days’. This expression makes it clear that customary rest days and holidays do not count as lay time. This would, for example, have the effect of excluding Fridays in Islamic countries. The expression ‘working day’ is a description of the type of day and is intended to draw a distinction between those days upon which work is habitually carried out at the port in question and those days which are considered to be days of rest or holidays. It is a day of 24 consecutive hours. It does not take into account the number of hours which are customarily worked at that port in any working day. Thus, it would not be open to the charterer to construe a clause in such a way that ‘working day’ meant a period of 24 hours consisting of two calendar days during which at the relevant port it was customary to work for 12 hours a day. A working day is a period of 24 hours which, in theory, starts at midnight on one day and finishes at midnight on the following day – effectively, a working calendar day. However, this is a presumption which may be displaced in the same way that a mere reference to ‘days’ will be calendar days unless there is something which makes it clear that the intention was that it should be any period of 24 hours. In circumstances where ‘working days’ do not commence at midnight, it is likely that before the expiry of a working day consisting of a period of 24 hours, a non-working day (such as a holiday or a Sunday) may begin. If that occurs, the ‘working day’ will then effectively be in two parts – the first part being from the commencement of lay time to midnight on that day and the second part being at midnight at the end of the holiday until the expiry of the 24 hours. Example: If the laytime provision is for conventional (as opposed to calendar) working days and Sunday is a non-working day in the relevant port, then where laytime commences at noon on Saturday, the first day of allowed laytime will run for 12 hours until midnight on the Saturday, will be interrupted for 24 hours (during Sunday) and will resume for a further 12 hours ending at noon on Monday.