Welcome to the forum, Dave Sangster.
I'm assuming you mean Humalin I, not Humalin R (100 = normal strength short acting; 500 = concentrated short acting, taken with meals), Humalin M3 (mixed short & long acting, taken twice a day).
On single long acting injection, minimum test times are before bedtime injection, when getting up and, assumig you drive, before each time setting off, plus every 2 hours on longer trips. If you have a driving licence, you need to inform DVLA, which will direct you to this advice, plus keeping hypoglycaemia remedies in car.