unstable link from my base station to my satellite

good morning  to every body,
i will first of all tell you that i'm a french speaker and i just try to speak and write english. so allow me to introduce some french word during my explanation.
so i manage a base station in cameroon  and our provider is skyvision; our vsat is pointing on amc12. the problem is that our ping vary hour from hour.  for example some day in the morning before 9oclock the ping from our dns  offer by sky is 600 to 650 ms but after 9h it pass to 1000ms ,1200ms , and some time to 1500ms. and some time they are some request time out.but in the night the ping recovers 600to 650ms.
please what could be the problem? because when this appear it disturb our service and then the QOS IS BAD. Please  is it some "appareil de mesure" to test our link with sky or with amc12?
i 'll tell you that we  provide many services like  internet, voip, vpn and so on to our customer.
what is the normal request time of ping from one base station on earth to one satellite.
please could some body help me?
thank you for your attention.
best regard.

thank you  ROHIT for your reply. but i'm  still waiting for other reesponse .
best regards.
merline from Cameroon.

we have this problem once. BUC not normally working or antenna pointing. Check parameters when ping growing up.