MS Project Custom Fields Formula calculate start in timezone with daylight saving

[BVOPP]

In Custom Fields type Date we now use the Formula:
ProjDateAdd([Start];"8h";"24 hours")
ProjDateAdd([Finish];"8h";"24 hours")

But we need to add a condition to check if Day Light Save is Winter or Summer because then the difference is not 8 hours but f.e. 9 hours

How can i do that?

[Aussiebear]

Unless the project takes place during the actual change over period the difference is still 8 hours from start to finish. You will normally just start and finish an hour earlier or later depending on which way the country adjusts its time clock.

[BVOPP]

We want to have the Central European Times and the Indian Times shown in MS Project for each task. So we need to calculate from CET to IST but the calculation is different when in Summer or Winter DayLight Saving zone.
I tried the below but that does not give me the correct result:

IIf(([Start]>11-3-2023 And [Start]<5-11-2023);ProjDateAdd([Start];"3,5h";"24 hours");ProjDateAdd([Start];"4,5h";"24 hours"))

It always gives the result for the last calculation meaning adding 4,5 hours.

Testing shows me that this works:

IIf(([Start]<[Current Date]);ProjDateAdd([Start];"3,5h";"24 hours");ProjDateAdd([Start];"4,5h";"24 hours"))

Also this gives a "better" result

IIf(([Start]<"15-8-2023");ProjDateAdd([Start];"3,5h";"24 hours");ProjDateAdd([Start];"4,5h";"24 hours"))

The calculation gives below result but for 4-8-23 it is still wrong, where as for 15-5-2023 it works

Start	Date5 (the formula)	Date6 (formula always add 4,5)
4-8-23 08:00	4-8-23 12:30	4-8-23 12:30
15-9-23 09:00	15-9-23 13:30	15-9-23 13:30
15-5-23 08:00	15-5-23 11:30	15-5-23 12:30

So i guess the issue is in the fixed date format that I use?

[BVOPP]

I got it... Thanks and sorry for the disturbance

IIf(([Start]>DateValue("11-3-2023")AND[Start]<DateValue("5-11-2023"));ProjDateAdd([Start];"3,5h";"24 hours");ProjDateAdd([Start];"4,5h";"24 hours"))

[Aussiebear]

Thank you for posting the solution so others can learn.