im afraid there is provision to use the abreviation m'night you can find it here
.http://www.dft.gov.uk/pgr/roads/tss/tsmanual/trafficsignsmanualchapter7th
S 12.8 of Traffic Signs Manual ch 7
12.8 12 noon and 12 midnight should be expressed
as “Noon” (or “Midday”) and “Midnight” (or
“M’night”) respectively. Where a time period spans
midnight, it should be expressed as two separate time
periods, the first commencing at midnight and the
second ending at midnight, unless the same time
period applies on every day of the week.
ask for the traffic order for that stree and see what turns up