Splitting the dose is definitely something that will help as well, so if it's easy for you to do, then do it. I always encourage my own clients to split their dosing when doses can equal out to 2iu or greater per administration. Regarding morning vs. night time dosing for water retention, it can definitely play a factor if that's your sole time of administration.
That being said, I would always encourage anyone experiencing water retention sides to evaluate basics first before turning to the HGH as the root or only cause. It can definitely play a factor, but if everything else is controlled it should be minimal. Check your BP regularly (you should be doing this anyway if you're on AAS as well) meaning at least once a week. Even if it's not out of range, if it's
close to the upper end of normal range, consider supplementing with an ARB such as Telmisartan which can also reduce water retention through the same mechanism by which it reduces BP. I always recommend an ARB anyways for most people on AAS, but that's beside the point here. The true basics should hopefully be within your control if you're using HGH/AAS but I know that isn't always the case, so evaluate your total fluid intake and sodium intake as well, make sure that they correlate and you aren't over-consuming salt. Even sleep quality can play a large factor with this, food sources, etc.
I know personal experience varies wildly but currently I have been holding my peak dosage of compounds for about six weeks after seven weeks of tapering up initially, another dose increase at 14 weeks, and a final escalation at 20 weeks (so, currently on week 26 of a push up/gain phase) which includes:
1200mg Test C/wk
1800mg Mast E/wk
350mg NPP / wk
12iu HGH/day split 4-4-4 waking, pre-workout, before bed (this dose has been constant throughout this push phase, so 12iu/d for 26 weeks)
Insulin as needed, currently about 10iu Lantus/day
No issues with bloat, water retention, or neuropathy. Also, for what it's worth, I personally never have needed or have had any clients need a hyper-conservative taper protocol for HGH. I know that's a bit of a long winded answer, more so than you were probably looking for, but hopefully it helps address the root cause.