Hello,

Your task can be achieved with two approaches: client-side and backend. In both cases, it would be better to create a new column in the Concert object in which you will store a value of the current combined duration of all Performances.
1) Client-side: to put it simply, you need to create a customization of a crt.CreateRecordRequest in which depending on your logic cancel the request (just not call next?.handle(request)) or allow it. In this customized CreateRecordRequest you need to read the current value of the created column (you can use ESQ or other mechanics) and the value of your system setting (const value = await sysSettingsService.getByCode('UsrSomeSetting');). if the first value is greater than the SysSetitng then cancel the request and display a message, if not, then run a next?.handler and increase the value of a column.

2) Backend: you need to write your own logic on onSaving event using the object designer or your own EventListener. In it just like in the first variant check the value of a column and SysSetting (you can also use ESQ) and cancel the request (do not run base.OnSaving) or allow it and increase the value of a column accordingly.

Hello,

Not sure about removing buttons (but theoretically it's possible using the "Visible" property), but as for the "Enabled" property, it's possible to control the state of the button. This can be achieved using sandbox messages exchange mechanisms like (control the copy button "Enabled" property in the detail on the case page based on the case category selected):

CasePage schema

messages: {
			"UpdateActionsStatuses": {
				mode: Terrasoft.MessageMode.PTP,
				direction: Terrasoft.MessageDirectionType.PUBLISH
			}
		},
		...
onCategoryChanged: function() {
				this.callParent(arguments);
				this.sandbox.publish("UpdateActionsStatuses", this.get("Category"), ["ForActionsStatusUpdate"]);
			}

Detail schema

messages: {
			"UpdateActionsStatuses": {
				mode: Terrasoft.MessageMode.PTP,
				direction: Terrasoft.MessageDirectionType.SUBSCRIBE
			}
		},
....
CopyRecordMenuItemEnabled: {
                    dataValueType: this.Terrasoft.DataValueType.BOOLEAN,
                    value: false
			},
....
getCopyRecordMenuItem: function() {
				return this.getButtonMenuItem({
					Caption: {"bindTo": "Resources.Strings.CopyMenuCaption"},
					Click: {"bindTo": "copyRecord"},
					Enabled: {bindTo: "CopyRecordMenuItemEnabled"},
					Visible: {bindTo: "IsEnabled"}
				});
			},
....
subscribeSandboxEvents: function() {
				this.callParent(arguments);
				this.sandbox.subscribe("UpdateActionsStatuses", this.updateActionsStatus, this,
						["ForActionsStatusUpdate"]);
			},
 
			updateActionsStatus: function(result) {
				var parentCaseCategory = result.displayValue;
				var isCategoryCorrect = parentCaseCategory == "PPE Case (Sales Contract)";
				this.updateCopyRecordMenuItem(isCategoryCorrect);
			},
 
			updateCopyRecordMenuItem: function(isCategoryCorrect) {
				var parentCopyRecordEnabled = this.getCopyRecordMenuEnabled();
				var isEnableCopyRecordMenuItem = isCategoryCorrect && parentCopyRecordEnabled;
				this.set("CopyRecordMenuItemEnabled", isEnableCopyRecordMenuItem);
			}

As a result the copy button will be enabled in the detail only if any record is selected in the detail and also if the case category (case page is where the detail is added) is "PPE Case (Sales Contract)".

Yes, it worked. Thank you