I hope I can help, lets see:
Agmatine has been shown to have Glucose Disposal effects on certain doses, one of them certainly being 1g. Now if you have breakfast, then 2 hours after that (your stomach is "empty") and you take agmatine, it might make you feel lightheaded if you are hypoglycemic OR if you have low pressure tendencies. However I have not seen much Blood Pressure effects on agmatine under 2g. Just to clarify, Hemavol DOES contain Agmatine Sulfate already , adding more agmatine might get you to the 2g range, hence you might be sensitive to the glucose drop in your blood or the BP lowering.
On another note, of course your pumps are going to be greater in the evening if you have been carb loading all day, glycogen replenishment, water absorption and the agmatine will go into equation to produce a substantial vasodilating effect at that point.
Now you mentioned you would feel bad with Agmatine Pre-workout (I have already addressed it up there , and I certainly do hope that's right :/) but when you eat up you fill up. This would be in regards to insulin sensitivity, disposing of glucose pre workout, using the glycogen storage in your muscles in a workout and then getting food in after it when you have been in a "low glucose" and high exercise state for a while , is going to have a "food pump" effect much like with GDAs, in which case...GREAT! Who doesn't enjoy food pumps?
Now a mild suggestion...how about you try 1g Agmatine WITH your pre workout meal (carb containing) and then you workout . 1-2g should be enough to get a good GDA-like response from the meal and help during the workout. Be it in the AM or the PM , take it with a meal, it by no means diminishes or tarnishes all the advantages of consuming agmatine.
Hope that helps! Perhaps higher minds can help more than me hehe.